As always, if anyone finds an error or omission in this post, please let me know so I can correct it!
So your TJ won't start...in fact, it won't even crank (or just barely struggles to turn over) and the lights in the vehicle dim when this is attempted. Well, read on to see if we can solve this problem PDQ. Note that, if you do not hear anything and/or the lights on your Jeep do not dim when you try to start it, you probably have a problem with the starter energizing circuit (like the starter switch) or the starter itself and this guide may not help you, or the battery. You can try skipping to step 16 to see if it may be your starter.
To perform these tests, you will need a multimeter. If you do not have a meter, you can buy one online (for your first meter, I'd just get a basic unit like this auto-ranging unit or, for even less, this manual range one). You can also pick up meters from hardware stores like this (admittedly cheesy) meter. You may even be able to get a loaner meter from your local auto parts store but I would not suggest buying one there as their prices are usually way out of line. For a bit more info on using a multimeter, see the first section of this thread. You will also need a sidekick to attempt to start the Jeep while you make the measurement with the meter (or vise-versa).
If your symptoms match what is described in the first sentence, what you are experiencing is almost certainly a bad connection or a bad battery. The trick is, knowing which and, if a connection, what connection. The following steps will determine that. Much of the following is predicated on the fact that you either hear an attempt at starting (click click or slow crank) and/or that the lights (dash/headlights) on the Jeep dim at that point. This indicates that the circuit that tells the starter to run is functioning but the problem is with the power being supplied by or from the battery.
1. Put the meter in DC volts mode (if the meter is not auto-ranging, select the 20 volt range) and put the leads on the battery terminals, directly on the battery, not on the cable terminal clamps. Put the black lead on the negative post and red lead on the positive post. Without attempting to start the Jeep, you should read something above 12.4 volts for a nominally charged battery. If it is below that, you should charge the battery before continuing.
2. While continuing to hold the meter on the battery terminals, have Tonto try to start the Jeep. The voltage reading should drop to no less than about 9.6 volts. If it drops below this (especially a if it's a lot below), your battery is bad, despite what the auto parts store may have told you or it is in serious need of a charge (but that is unlikely if its resting voltage is 12.4 volts or higher).
3. If it does not drop below 9.6 volts, then we need to start moving out from the battery. In reality, if your battery is good, you will probably have far less voltage drop than 9.6 V because not much current is actually being pulled from the battery, due to the not-yet-located bad connection. Place you meter's black lead on the battery's negative terminal as before, but put the red lead on the cable clamp/connector on the positive side and repeat the starting attempt (if your battery cable is separate from the clamp as shown in the pic below, make sure you put your lead on the clamp, not the cable end connector or the bolt connecting them). If the voltage drops below 9.6 volts (probably a lot lower) here, you have a bad connection between the positive clamp and the battery. Make sure it is tight and free of corrosion and test again. A broken clamp like the one shown below can cause this issue. When tight, you should not be able to turn the clamp around the terminal by hand (or using a tools either, but don't go that far or you can break the post off of the battery).
If cleaning and tightening the clamp does not resolve the problem, the clamp is probably broken and/or stretched out to the point where it is not making firm enough contact to the battery. Also retest the battery drop by repeating step 2, just to make sure. If the clamp does test bad, you will need to replace either the clamp (if separate from the cable) or the entire cable/clamp assembly or a clamp and cable set. If you need to replace your terminal clamps, I highly suggest the military style shown below as they allow good connections and give plenty of room for aftermarket connections like winches or high-power audio equipment, paired with a quality eyelet-to-eyelet cable.
A type of clamp to definitely avoid is this...because they suck foamy, brown donkey spit! The connection between the clamp and the cable will never be better than mediocre, at best.
4. If the positive cable clamp passes muster, do the same for the negative cable. Put the red lead directly on the battery's positive terminal and the black lead on the negative side cable clamp and tell Watson try to start the Jeep again. If the voltage drops below 9.6 volts (again, probably a lot lower) here, you have a bad connection between the negative clamp and the battery. As before, make sure it is tight and free of corrosion and test again. See step 3 for remedies.
If your cables are single-piece (no connections between the cable and the terminal clamp) like the one pictured below, skip to step 6.
5. If both cable clamps test OK, we need to check the connections from the clamps to the cables. Repeat steps 3 and 4 but, this time, place the lead that went to the clamp in those steps to the cable end connector that is bolted to the clamp. If you have a voltage drop below 9.6 volts when Robin tries to start it, then the connection between the cable terminal clamp and the cable end is bad. Remove, clean, and reattach the connection, making sure it is tight, and retest. If it still fails, you probably are not getting everything clean. If you have bad corrosion, you may need to replace the terminal clamp, the cable, or both.
6. If we still don't show a voltage drop below 9.6 volts, we need to move on to checking the cables themselves. The negative cable should have multiple wires in it (ignoring anything aftermarket that may be connected to the negative terminal clamp, like a cable to a winch or audio equipment) but the biggest wire (or one of the big ones) will go from the battery, directly to the engine block. If you do not have a big wire going from the negative terminal clamp on the battery to the engine block, your TJ has been incorrectly rewired and you should post a request (a new post, not a reply to this one) for more assistance as some more specific photos and instructions will be in order. Once you find the cable going to the engine block, connect your meter with the red lead on the positive terminal of the battery and the black lead on the cable end connection that is bolted to the block (not the bolt or the block). Make sure you get a good connection with your leads because you may be working with a pretty grungy area here. Without trying to start the Jeep, you should read within .1 volts or so of the voltage you read in step 1. If it is quite a bit lower, you almost certainly have a bad negative cable...but you can do the next step to confirm.
7. Being careful not to put your body or your clothing anywhere near moving parts while holding the meter leads, just in case the Jeep decides to actually start, have Kato try to start the vehicle. If the voltage reading drops from your no-crank voltage above 12 volts to below 9.6 volts (again, it will probably be way below that), then your negative battery cable is bad and needs to be replaced. To be specific, the problem is likely in one of the cable's ends where a bad crimp or corrosion is keeping the cable from performing its assigned duties. If you have to replace your cable(s), this is again a good time to consider switching to the military style terminal clamps and some upgraded 2 gauge (or bigger) cables.
8. If no drop below 9.6 volts there, move the negative lead to the actual engine block. Again, you may need to really push and scratch with your meter lead to get a good connection...a reading that is not within .2 or so volts of what you read directly across the battery either indicates that your cable-to-block connection is really bad or that your lead is not making good contact with the block. Once you're certain you have solid contact to the block with your lead, read the voltage without attempting to start...if it's more than .2 volts below the battery voltage, you almost certainly have a bad connection to the block but you can do the next step to verify.
9. Keeping the meter leads on the battery positive and the block, tell your whipping boy...er...sidekick, to try to start the Jeep. If the voltage reading drops below 9.6 volts, you have a bad connection between the cable end and the block...remove the cable, clean it and the connection point on the block, put it back on, bless it (a Priest is handy here), and test again. If it still fails, you are probably dealing with a badly corroded cable end connection or a badly corroded/rusted connection point on the block...pull out a can o' whoopass (tell the Priest to look away) and clean the snot out of everything again and/or replace the negative cable if necessary.
10. Another good sized wire from the negative terminal clamp should go to the chassis (body) at what will typically be a bolt on the firewall, just behind the passenger side (for a LHD Jeep) of the engine. Perform the same test here, just to make sure it's good. Cleaning this connection can't hurt.
11. OK, so the negative wires check OK...let's go on to the positive side. Start by placing the black lead of your meter directly on the negative terminal of the battery and the red on the terminal clamp on the positive side. Your no-crank voltage should be pretty much the same as the voltage directly across the battery terminals. Now, have Sancho try to start the Jeep. If the voltage drops below 9.6 volts, you have a bad connection between the battery terminal and the terminal clamp...remove, clean, reattach, retest and replace the clamp and/or cable if necessary.
12. Alright, the positive connection clamp seems good. Now move the red meter lead to the positive cable's end connection and test voltage again (static and attempting to start). If you drop below 9.6 volts, there's an issue with the connection between the cable end and the terminal clamp. Clean, disinfect, bless or curse at your discretion, reattach, tighten and test again. If it still fails, you must have bad corrosion or a loose connection, replace the clamp and/or cable as needed.
13. Ewwwwwwwww...step 13! Yeah, whatever.
14. Ahright, you still do not show a big voltage drop when testing at the positive cable end connection to the clamp...let's move on to the other end of the positive cable. The big (or one of the big) wires from the positive cable should go directly to the starter. The other big wire should go to the alternator but we don't care about it as it has nothing to do with starting the Jeep...just charging the battery and supplying current from the alternator when the engine IS running. Keeping the black meter lead on the negative battery terminal, place the red lead on the cable end connector that is connected to the starter (the cable connector, not the bolt on the starter). Again, make sure you body, clothing, hair, and karma are not in a position to get bitten by moving parts should the Jeep decide to start and, once again, have Baldrick try to start the beast. If you see the voltage drop below 9.6 volts here, it indicates that the positive cable (probably an end connection) is bad and you should replace it.
15. We're on the proverbial home stretch now! If you still saw no big voltage drop at the positive cable end connector on the starter side of the cable, put the red meter lead on the actual bolt on the starter where the positive cable connects and, again, verifying nothing within your sphere of influence is within the range of possible moving parts and have "Precious" attempt to start the Jeep. If you see the voltage drop below 9.6 volts here, the connection between the positive cable end and the starter is bad...remove, clean, degrunge, and reconnect, making sure it's good and tight...then test again. If it still shows the excessive voltage drop you may need to go medieval on its ass to get things really clean and/or replace the positive cable if necessary.
16. If you show 9.6 volts or more at the positive connector of your starter, try (just to verify) putting the black meter lead to the engine block and the red to the starter positive bolt and try to start. If it still shows 9.6 volts or more, your starter is bad; sorry! Again, this assumes that you are hearing the starter click or the lights are dimming. If you do not see any real voltage drop, your starter is probably still bad (open / bad solenoid) but that, by itself, would not cause the Jeeps lights to dim and you certainly would not have any clicking or cranking attempts from the starter. You can check for the solenoid being activated by putting meter's black lead on the battery negative and the read lead on the solenoid connector that goes to the ignition. This can be a screw-on type like the center (silver) connector on the starter below or...
...like this
...a plug-in spade connector like this one.
At any rate, it will be the third (smallest) connector on the solenoid, with the other two going to the positive battery cable and to a cable or bar that goes into the starter motor. Slap yo meter's red lead on that connection while R2 tries to start the Jeep. You should see 12+ volts at that connector whenever the key is turned to the start position. If not, try cleaning that connection and test again. If still no 12 volts, your problem is in the starter energizing circuit but, if so, you will NOT hear the starter click and it will NOT try to crank.
If all of the above did not help you satisfactorily solve your problem, please make a post and we will gladly jump in to make more suggestions!
So your TJ won't start...in fact, it won't even crank (or just barely struggles to turn over) and the lights in the vehicle dim when this is attempted. Well, read on to see if we can solve this problem PDQ. Note that, if you do not hear anything and/or the lights on your Jeep do not dim when you try to start it, you probably have a problem with the starter energizing circuit (like the starter switch) or the starter itself and this guide may not help you, or the battery. You can try skipping to step 16 to see if it may be your starter.
To perform these tests, you will need a multimeter. If you do not have a meter, you can buy one online (for your first meter, I'd just get a basic unit like this auto-ranging unit or, for even less, this manual range one). You can also pick up meters from hardware stores like this (admittedly cheesy) meter. You may even be able to get a loaner meter from your local auto parts store but I would not suggest buying one there as their prices are usually way out of line. For a bit more info on using a multimeter, see the first section of this thread. You will also need a sidekick to attempt to start the Jeep while you make the measurement with the meter (or vise-versa).
If your symptoms match what is described in the first sentence, what you are experiencing is almost certainly a bad connection or a bad battery. The trick is, knowing which and, if a connection, what connection. The following steps will determine that. Much of the following is predicated on the fact that you either hear an attempt at starting (click click or slow crank) and/or that the lights (dash/headlights) on the Jeep dim at that point. This indicates that the circuit that tells the starter to run is functioning but the problem is with the power being supplied by or from the battery.
1. Put the meter in DC volts mode (if the meter is not auto-ranging, select the 20 volt range) and put the leads on the battery terminals, directly on the battery, not on the cable terminal clamps. Put the black lead on the negative post and red lead on the positive post. Without attempting to start the Jeep, you should read something above 12.4 volts for a nominally charged battery. If it is below that, you should charge the battery before continuing.
2. While continuing to hold the meter on the battery terminals, have Tonto try to start the Jeep. The voltage reading should drop to no less than about 9.6 volts. If it drops below this (especially a if it's a lot below), your battery is bad, despite what the auto parts store may have told you or it is in serious need of a charge (but that is unlikely if its resting voltage is 12.4 volts or higher).
3. If it does not drop below 9.6 volts, then we need to start moving out from the battery. In reality, if your battery is good, you will probably have far less voltage drop than 9.6 V because not much current is actually being pulled from the battery, due to the not-yet-located bad connection. Place you meter's black lead on the battery's negative terminal as before, but put the red lead on the cable clamp/connector on the positive side and repeat the starting attempt (if your battery cable is separate from the clamp as shown in the pic below, make sure you put your lead on the clamp, not the cable end connector or the bolt connecting them). If the voltage drops below 9.6 volts (probably a lot lower) here, you have a bad connection between the positive clamp and the battery. Make sure it is tight and free of corrosion and test again. A broken clamp like the one shown below can cause this issue. When tight, you should not be able to turn the clamp around the terminal by hand (or using a tools either, but don't go that far or you can break the post off of the battery).
If cleaning and tightening the clamp does not resolve the problem, the clamp is probably broken and/or stretched out to the point where it is not making firm enough contact to the battery. Also retest the battery drop by repeating step 2, just to make sure. If the clamp does test bad, you will need to replace either the clamp (if separate from the cable) or the entire cable/clamp assembly or a clamp and cable set. If you need to replace your terminal clamps, I highly suggest the military style shown below as they allow good connections and give plenty of room for aftermarket connections like winches or high-power audio equipment, paired with a quality eyelet-to-eyelet cable.
A type of clamp to definitely avoid is this...because they suck foamy, brown donkey spit! The connection between the clamp and the cable will never be better than mediocre, at best.
4. If the positive cable clamp passes muster, do the same for the negative cable. Put the red lead directly on the battery's positive terminal and the black lead on the negative side cable clamp and tell Watson try to start the Jeep again. If the voltage drops below 9.6 volts (again, probably a lot lower) here, you have a bad connection between the negative clamp and the battery. As before, make sure it is tight and free of corrosion and test again. See step 3 for remedies.
If your cables are single-piece (no connections between the cable and the terminal clamp) like the one pictured below, skip to step 6.
5. If both cable clamps test OK, we need to check the connections from the clamps to the cables. Repeat steps 3 and 4 but, this time, place the lead that went to the clamp in those steps to the cable end connector that is bolted to the clamp. If you have a voltage drop below 9.6 volts when Robin tries to start it, then the connection between the cable terminal clamp and the cable end is bad. Remove, clean, and reattach the connection, making sure it is tight, and retest. If it still fails, you probably are not getting everything clean. If you have bad corrosion, you may need to replace the terminal clamp, the cable, or both.
6. If we still don't show a voltage drop below 9.6 volts, we need to move on to checking the cables themselves. The negative cable should have multiple wires in it (ignoring anything aftermarket that may be connected to the negative terminal clamp, like a cable to a winch or audio equipment) but the biggest wire (or one of the big ones) will go from the battery, directly to the engine block. If you do not have a big wire going from the negative terminal clamp on the battery to the engine block, your TJ has been incorrectly rewired and you should post a request (a new post, not a reply to this one) for more assistance as some more specific photos and instructions will be in order. Once you find the cable going to the engine block, connect your meter with the red lead on the positive terminal of the battery and the black lead on the cable end connection that is bolted to the block (not the bolt or the block). Make sure you get a good connection with your leads because you may be working with a pretty grungy area here. Without trying to start the Jeep, you should read within .1 volts or so of the voltage you read in step 1. If it is quite a bit lower, you almost certainly have a bad negative cable...but you can do the next step to confirm.
7. Being careful not to put your body or your clothing anywhere near moving parts while holding the meter leads, just in case the Jeep decides to actually start, have Kato try to start the vehicle. If the voltage reading drops from your no-crank voltage above 12 volts to below 9.6 volts (again, it will probably be way below that), then your negative battery cable is bad and needs to be replaced. To be specific, the problem is likely in one of the cable's ends where a bad crimp or corrosion is keeping the cable from performing its assigned duties. If you have to replace your cable(s), this is again a good time to consider switching to the military style terminal clamps and some upgraded 2 gauge (or bigger) cables.
8. If no drop below 9.6 volts there, move the negative lead to the actual engine block. Again, you may need to really push and scratch with your meter lead to get a good connection...a reading that is not within .2 or so volts of what you read directly across the battery either indicates that your cable-to-block connection is really bad or that your lead is not making good contact with the block. Once you're certain you have solid contact to the block with your lead, read the voltage without attempting to start...if it's more than .2 volts below the battery voltage, you almost certainly have a bad connection to the block but you can do the next step to verify.
9. Keeping the meter leads on the battery positive and the block, tell your whipping boy...er...sidekick, to try to start the Jeep. If the voltage reading drops below 9.6 volts, you have a bad connection between the cable end and the block...remove the cable, clean it and the connection point on the block, put it back on, bless it (a Priest is handy here), and test again. If it still fails, you are probably dealing with a badly corroded cable end connection or a badly corroded/rusted connection point on the block...pull out a can o' whoopass (tell the Priest to look away) and clean the snot out of everything again and/or replace the negative cable if necessary.
10. Another good sized wire from the negative terminal clamp should go to the chassis (body) at what will typically be a bolt on the firewall, just behind the passenger side (for a LHD Jeep) of the engine. Perform the same test here, just to make sure it's good. Cleaning this connection can't hurt.
11. OK, so the negative wires check OK...let's go on to the positive side. Start by placing the black lead of your meter directly on the negative terminal of the battery and the red on the terminal clamp on the positive side. Your no-crank voltage should be pretty much the same as the voltage directly across the battery terminals. Now, have Sancho try to start the Jeep. If the voltage drops below 9.6 volts, you have a bad connection between the battery terminal and the terminal clamp...remove, clean, reattach, retest and replace the clamp and/or cable if necessary.
12. Alright, the positive connection clamp seems good. Now move the red meter lead to the positive cable's end connection and test voltage again (static and attempting to start). If you drop below 9.6 volts, there's an issue with the connection between the cable end and the terminal clamp. Clean, disinfect, bless or curse at your discretion, reattach, tighten and test again. If it still fails, you must have bad corrosion or a loose connection, replace the clamp and/or cable as needed.
13. Ewwwwwwwww...step 13! Yeah, whatever.
14. Ahright, you still do not show a big voltage drop when testing at the positive cable end connection to the clamp...let's move on to the other end of the positive cable. The big (or one of the big) wires from the positive cable should go directly to the starter. The other big wire should go to the alternator but we don't care about it as it has nothing to do with starting the Jeep...just charging the battery and supplying current from the alternator when the engine IS running. Keeping the black meter lead on the negative battery terminal, place the red lead on the cable end connector that is connected to the starter (the cable connector, not the bolt on the starter). Again, make sure you body, clothing, hair, and karma are not in a position to get bitten by moving parts should the Jeep decide to start and, once again, have Baldrick try to start the beast. If you see the voltage drop below 9.6 volts here, it indicates that the positive cable (probably an end connection) is bad and you should replace it.
15. We're on the proverbial home stretch now! If you still saw no big voltage drop at the positive cable end connector on the starter side of the cable, put the red meter lead on the actual bolt on the starter where the positive cable connects and, again, verifying nothing within your sphere of influence is within the range of possible moving parts and have "Precious" attempt to start the Jeep. If you see the voltage drop below 9.6 volts here, the connection between the positive cable end and the starter is bad...remove, clean, degrunge, and reconnect, making sure it's good and tight...then test again. If it still shows the excessive voltage drop you may need to go medieval on its ass to get things really clean and/or replace the positive cable if necessary.
16. If you show 9.6 volts or more at the positive connector of your starter, try (just to verify) putting the black meter lead to the engine block and the red to the starter positive bolt and try to start. If it still shows 9.6 volts or more, your starter is bad; sorry! Again, this assumes that you are hearing the starter click or the lights are dimming. If you do not see any real voltage drop, your starter is probably still bad (open / bad solenoid) but that, by itself, would not cause the Jeeps lights to dim and you certainly would not have any clicking or cranking attempts from the starter. You can check for the solenoid being activated by putting meter's black lead on the battery negative and the read lead on the solenoid connector that goes to the ignition. This can be a screw-on type like the center (silver) connector on the starter below or...
...like this
...a plug-in spade connector like this one.
At any rate, it will be the third (smallest) connector on the solenoid, with the other two going to the positive battery cable and to a cable or bar that goes into the starter motor. Slap yo meter's red lead on that connection while R2 tries to start the Jeep. You should see 12+ volts at that connector whenever the key is turned to the start position. If not, try cleaning that connection and test again. If still no 12 volts, your problem is in the starter energizing circuit but, if so, you will NOT hear the starter click and it will NOT try to crank.
If all of the above did not help you satisfactorily solve your problem, please make a post and we will gladly jump in to make more suggestions!
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