Working through final wiring issues on my build and I'm stumped
- Thread starter Gormy
- Start date
My intent is not to silence anyone, so please, do chime in. Just please try not to distract from a systematic approach. Complex problems require such. Going off on tangents - while sometimes, when combined with a bit of luck, can yield big dividends - is not as productive.
@Gormy:
I want to get to the question I asked, but first, I want to make sure you're interpreting your multimeter correctly. One of your last posts makes me think that you are not. At the 200 setting, with 0.4 on the screen, how many ohms are you reading that as:
That's 0.4 ohms on most meters. In fact, all digital meters I've ever used. I'm not saying you're wrong because I've never used your meter. However, I downloaded the instructions for it, and there's no mention that the reading needs to be multiplied by a scale factor depending on the dial setting. The reason meters have different scales is due to how they work. They are digital devices used to measure an analog signal. Inside, there is a chip called an analog-to-digital converter. Due to limitations in that chip, they put a scale selector on their to make it useful for measure a 2 ohm resistor and a 2,000,000 ohm resistor (the upper limit of that meter's range). If there was no selector, and it was still capable of measuring 2,000,000 ohms, it wouldn't be able to measure anything even close to 1 ohm. In fact, on the 2000k setting, it can only detect at about 1,000 ohm increments.
We first need to figure out how to read your meter, and then we need to reconsider whether the numbers you've been sharing are the number on the meter, or the number you calculated.
I want to get to the question I asked, but first, I want to make sure you're interpreting your multimeter correctly. One of your last posts makes me think that you are not. At the 200 setting, with 0.4 on the screen, how many ohms are you reading that as:
That's 0.4 ohms on most meters. In fact, all digital meters I've ever used. I'm not saying you're wrong because I've never used your meter. However, I downloaded the instructions for it, and there's no mention that the reading needs to be multiplied by a scale factor depending on the dial setting. The reason meters have different scales is due to how they work. They are digital devices used to measure an analog signal. Inside, there is a chip called an analog-to-digital converter. Due to limitations in that chip, they put a scale selector on their to make it useful for measure a 2 ohm resistor and a 2,000,000 ohm resistor (the upper limit of that meter's range). If there was no selector, and it was still capable of measuring 2,000,000 ohms, it wouldn't be able to measure anything even close to 1 ohm. In fact, on the 2000k setting, it can only detect at about 1,000 ohm increments.
We first need to figure out how to read your meter, and then we need to reconsider whether the numbers you've been sharing are the number on the meter, or the number you calculated.
Well that would be my inexperience and not fully understanding how to read it. I thought I had read online that there was still a multiplication needed for2 200, but I likely read that wrong. I'm sorry for causing us extra work.
How you read it on the screen is how it is when it is hooked up. Take my mistake out, and from your reply, that means this is 0.4 ohms?
When the wire was broken at C154, and I had to have it on the 20k setting, what was it reading when it was at 0.76?
I'm really sorry for steering us wrong. I am much better at the mechanicals than I am electrical.
Ok, it's been a busy day, so I haven't had much free time. I called Gardner Bender and talked to tech support. The very nice rep confirmed my suspicions - whatever the display reads is the resistance value. Do not scale it manually. So, with that behind us, we'll have to trudge forward. Unfortunately, the busy day will continue, so my responses will be sporadic for a bit.
If the display reads, "0.4" that means 0.4 ohms, no matter the dial setting.
Now this confuses me again. On the 20k setting, it shouldn't have a decimal point. Are you sure you're getting a reading of "0.76" when on 20k?
What is the reading with the probes not touching anything (or each other)?
No worries - it's part of the learning process!
Well, then let's continue to work through this so you can stop saying that sometime in the future!
Gormy, I was just thinking. While a thread like this is very helpful to all the readers who find it in the future, it's slow-going trying to work through this in written form. Perhaps we could go to phones and work through it this weekend? Weekends are the only time I can dedicate blocks of time to something. If that works, PM me your phone number and times you are available this weekend. After we solve it, and I'm confident we can do so, we can come back and post what happened for the benefit of the readers. That work for you?
Back to my question. Trying to stay with the Socratic method, but it's tough for me. Think about what you were measuring when you put your meter probes on Pins 1 and 3 with C154 unplugged. With it unplugged, the Manual Transmission Jumper, which is the black loop on the mating connector, is missing. So, this is what the wiring circuit looks like with that jumper removed, and your probes at pins 1 and 3 (shown by the red and black arrows):
Looking at that schematic, what are the probes measuring? Anyone? Bueller, Bueller? (that economics teacher was definitely Socratic, too!)
I've reread through the thread again this morning, along with my first cup of coffee. I noticed something in one of your pictures. You took a pretty nice close up of the ground location on the block (and G105). I circled them in the pic below:
In the blue circle, I see corrosion (the green stuff). That is G105. Please take a resistance measurement between that ring terminal and G154, pin 1. I would guess that to be relatively high resistance.
In the orange circle, I see some frayed wires. I don't think that is causing an issue, but it IS the main engine ground back to the battery, so Its carrying the load from the starter. I'd probably get some new battery cables, once you get this figured out.
In the blue circle, I see corrosion (the green stuff). That is G105. Please take a resistance measurement between that ring terminal and G154, pin 1. I would guess that to be relatively high resistance.
In the orange circle, I see some frayed wires. I don't think that is causing an issue, but it IS the main engine ground back to the battery, so Its carrying the load from the starter. I'd probably get some new battery cables, once you get this figured out.
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That's a good catch, Mike_H. Exactly the type of thing that can cause a bad ground.
Thanks for pointing this out. I will plan to replace these wires as part of this process.
I've been racking my brain trying to think of anything else I missed. As I mentioned, the engine and wire harness all came out of the same vehicle, and from the best I can tell, everything is back where it was previously. But just this morning something popped into my head when I was trying to figure out what I have changed as I swapped it over, and I can't believe I left this out of my posts. I really, really hope this isn't the issue (well I do because it would fix it, but I don't want to feel so stupid for overlooking it).
When I disassembled the old Jeep I removed the A/C system. It was not functioning properly, the coolant was gone, and with my plans to never have the top and doors on this, there's no point in keeping it. I am going to change the compressor over to an OBA system in time. For now the wire harness that plugged into the AC accumulator at the firewall is not plugged into anything. The wire harness at the compressor is still plugged in.
I don't think that's an issue, but wanted to throw that out there just in case it sparks any ideas. From looking at the schematics, I don't think there's anything in the accumulator harness that would cause this.
New windshield just went in this morning. Hoping to fix and paint the rollbar this weekend. Then it's 95% ready to go!
When I disassembled the old Jeep I removed the A/C system. It was not functioning properly, the coolant was gone, and with my plans to never have the top and doors on this, there's no point in keeping it. I am going to change the compressor over to an OBA system in time. For now the wire harness that plugged into the AC accumulator at the firewall is not plugged into anything. The wire harness at the compressor is still plugged in.
I don't think that's an issue, but wanted to throw that out there just in case it sparks any ideas. From looking at the schematics, I don't think there's anything in the accumulator harness that would cause this.
New windshield just went in this morning. Hoping to fix and paint the rollbar this weekend. Then it's 95% ready to go!
So if the ohms across the entire path are 0.4 ohms, that's not a bad ground, correct? You mentioned it should be at 0 or close to it, but that wires do have some resistance in them. So through several feet of wiring, is that resistance okay?
Correct. I went back and looked at my picture. At the 20k reading it was 0.76. There was a decimal.
It says 1. or just 1 I think, the "infinite resistance" default it goes to.
Again, thank you for all the time and energy you're spending on this.
The wires that plug into the compressor share a ground point with the stuff we're talking about (its splice 132 in the Diagram on post 37). That is what powers the A/C clutch. The connector that is plugged (or not, in your case) into the accumulator is a pressure switch, if I'm not mistaken, so it shouldn't be related to the issues you're having with not starting.
Have you had a chance to measure the resistance between G105 and the Manual Trans jumper wire?
That's what I figured. But wanted to double check as it's the only other thing I can think of that I changed.
Not yet. I have back to back to back meetings today. I will test that this afternoon.
If you really wanted, you could look the A/C system up. I would assume you could make the vehicle think its OK by connecting the two pins together, but I don't want to tell you to just try it without having you look it up to see if its normally open or normally closed. Its typically a safety for the A/C...if the switch isn't in the right state, it won't allow the A/C clutch to engage and build pressure in the system.
But that is another discussion for another thread
I don't think that would cause a problem, but I haven't looked at the schematics for that.
No, I wouldn't necessarily say 0.4 ohms is okay. See point 2 in Post #83. Unless that entire path is 40' of wire, that's too much resistance, and with the small amount of current from the meter, compared to the higher current when the relay coil energizes, that may be enough to indicate a problem. A test light on that circuit might provide more information. If it won't light, or is dim, it would show that the ground circuit isn't working.
Well, that's a head-scratcher. Usually, on 20k, there wouldn't be any decimals, and certainly, it shouldn't be more precise at 20k than 200, which only displays one decimal place. I'll explain a little more about the analog-to-digital (A2D) converter chip, and how it works, but be prepared, you're about to travel down a geeked-out engineering rabbit hole. Buckle up.
Your meter is a "GDT-11." I think the 11 means that it has an 11 bit A2D chip in it due to the scale breakdown on the dial, and based on a tenths decimal place when in 200 ohm mode. Here's how I jumped to that conclusion. The number of bits of an analog-to-digital chip tells you how big the measurement interval is. Each bit is a unit of measure. On the 200 setting, since you have tenths of an ohm capability, that means in absolute value terms, that the minimum value is 0.1 ohms and the max is 200.0 ohms, in 0.1 ohm increments. Bits are powers of 2. Two raised to the 11th power is 2048. If you go from 0.1 to 200.0 by 0.1 increments, there are 2000 possibilities (not counting zero). That's very close to 2048.
What the 11 bit A2D chip does, is whatever dial setting you use, it divides that number by 2049 (because zero counts, so you add 1 to the 2048), and that's your increment of measurement. As you change the dial, the minimum increment changes. This is called the resolution. There may be some other circuitry that does other conditioning and display values in between these increments, but that would just be manipulation of the numbers, not actual measurement. I'm not an electrical engineer, so my understanding is incomplete. So, here is the increment of measurement for each dial setting:
200 ohm is 0.1 ohms (slightly less, actually, but the display won't show hundreths of an ohm)
2000 ohms is 1 ohm
20k ohms is 10 ohms
200k ohms is 98 ohms
2000k ohms is 977 ohms
So, to see "0.76 ohms" on the display for the 20k setting is odd. It should jump from 0 ohms to 10 ohms, and display nothing between them because the 11 bit A2D chip can't discern a difference smaller than 10 ohms on the 20k setting. Weird!
I'd call GB back, but the tech I spoke to said that your meter was discontinued some time ago, and they have very little information on it. I don't think he'd be able to explain it to me.
Suggestion...do you have a neighbor with another multimeter you could compare results with? With another meter we could quickly see if there's any discrepancy between the two...there will be some...
I actually have a couple of resistors left over from a project...500 ohm. Any time I buy a cheap meter...and I have one in just about every vehicle...I check that resistor to see how close the meter is. I've returned a couple...I think one said 210 ohms and it went straight back to the store.
-Mac
I actually have a couple of resistors left over from a project...500 ohm. Any time I buy a cheap meter...and I have one in just about every vehicle...I check that resistor to see how close the meter is. I've returned a couple...I think one said 210 ohms and it went straight back to the store.
-Mac
What color is the tolerance band on that resistor? If it doesn't have one, which is common, it's only a 20% resistor, meaning the actual value will be between 400 and 600 ohms. Silver is 10% and gold is 5%. There are other colors for higher precision, but those are usually special order and pricey.