Bad alternator or gauge cluster?

nbarb

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Sep 24, 2020
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Texas
I couldn't find anything else on the forum with a similar list of symptoms to what my Jeep is going through, so I figured I'd post.
I hope this is obvious for someone smarter than I am

I was driving from south Dallas to north Dallas when this happened:
First sign I noticed was "check gauges" light turned on, then my battery voltage drops to 0 on gauge cluster.
However, my headlights and interior lights still worked. Car was still running, so I kept driving.
Battery drain came slowly, was able to drive about 45 minutes before having to pull over because my headlights and gauge cluster became too dim to read.
Turned car off, wouldn't crank again. Battery voltage still at 0, check gauges still on. Interior lights were still bright, though.
Got a jump start, made it home.

Now, when I first turn the key in my car, the battery reads around 11V, then dips to 0 and check gauges turns on.

I read somewhere on here that the alternator doesn't charge the battery without some condition being met from the gauge cluster. Does that sound right?

Attached pics of alternator and gauge cluster

tempImagehpEwjM.png


tempImageBqjZ7G.png


tempImagehsZGA4.png
 
The battery is now dead. I'd have the alternator tested, it sounds like the alternator went dead first with the battery following. If the alternator tests ok I'd be suspicious of the alternator's voltage regulator which is inside the PCM on the firewall. When the PCM's voltage regulator goes bad that causes the alternator to stop working.

Your problem has nothing to do with the instrument cluster.
 
The battery is now dead. I'd have the alternator tested, it sounds like the alternator went dead first with the battery following. If the alternator tests ok I'd be suspicious of the alternator's voltage regulator which is inside the PCM on the firewall. When the PCM's voltage regulator goes bad that causes the alternator to stop working.

Your problem has nothing to do with the instrument cluster.
I went ahead and replaced the alternator, didn’t work out. I’ll take a look at the PCM tomorrow. My jeep is a 1997 so iirc it has a fuse (thin wire) outside the alternator in the black box. Do you think it’s possible that tripped?

I might do an external voltage regulator if it’s the PCM.
 
The thin wire (called a fusible link) is in the charge wire leading to the battery from the alternator Doing a continuity test of that wire will show if it's intact or not.
 
Just an update for anyone that comes across this later:

Ended up being the voltage regulator in the PCM. If this happens to you do not buy a new pcm, it’s a waste of time and money and the part you end up with may not even work with your car. I bought one from FSOne and it didn’t work with my car and they don’t accept returns. Go buy an external voltage regulator. There’s posts on here about which ones to go with
 
Just an update for anyone that comes across this later:

Ended up being the voltage regulator in the PCM. If this happens to you do not buy a new pcm, it’s a waste of time and money and the part you end up with may not even work with your car. I bought one from FSOne and it didn’t work with my car and they don’t accept returns. Go buy an external voltage regulator. There’s posts on here about which ones to go with
FS1 is a shitty source for PCMs, the only good source I'm aware of for a replacement or a repair of a PCM is www.wranglerfix.com.
 
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Just an update for anyone that comes across this later:

Ended up being the voltage regulator in the PCM. If this happens to you do not buy a new pcm, it’s a waste of time and money and the part you end up with may not even work with your car. I bought one from FSOne and it didn’t work with my car and they don’t accept returns. Go buy an external voltage regulator. There’s posts on here about which ones to go with

I have the same issue with my instrument cluster can you tell me how you to install an external voltage regulator and which one to buy. Hopefully that works for me. Thanks