Dash Harness Troubleshooting

[brbluesman]

I've had a problem with my electrical for 3 years now and can't nail it down. I know there's a short somewhere but can't find it. I've replaced everything except the harness. I've got another used harness that I may swap out but was hoping I could find the problem. Everything works except my fuel gauge sometimes peaks out. Last night it went out completely. I believe it's a short because the fuel gauge would be on whenever the battery was connected. So I began disconnecting the battery whenever I parked to be cautious.
My weakest skills are electrical. I have a volt meter but not sure how to use it to find the problem. I'm going to try to test the fuel gauge today to see if it may be blown now. I know it's not the sending unit. That's brand new.
I could use some basic tips on how to troubleshoot. Thanks in advance.

[brbluesman]

Forgot to add an important note - my turn signals work when I first start the engine but soon after driving a bit, they don't come on. I would assume this is related to the above.

[chargervic]

Hello. Do your other gauges work? You can check your voltage limiter . It provides 5V to all your gauges . If it shorts out , it will send 12V to your gauges and show needles to the far right .

[brbluesman]

All the other gauges work fine. Only the Fuel gauge would act up. Sometimes it would work normally. Then driving for a bit it would peg out. Now it won't move at all, which makes me think it burned up. When the battery was connected it stayed on even when the ignition was off. None of the other gauges did anything like that. Then there's the turn signals that work when the I first start driving but after about 15 mins they don't work. So strange that only those to pieces are having an electrical problem.

[DynoDave]

Feb 29, 2016 22:10:16 GMT -5 brbluesman said:

Only the Fuel gauge would act up. Sometimes it would work normally. Then driving for a bit it would peg out. Now it won't move at all, which makes me think it burned up.

My guess would be that your cluster still has it's original, mechanical voltage limiter (your gauges don't actually work on 12 volts, but 5 volts). It is failing, allowing the voltage to spike, creating the surge in your gauges. And, when voltage has peaked above 5v, it has taken out your gas gauge.

Just a guess.

There are modern, stable, solid state replacements for the regulator.

[Deleted]

What does not make sense to me is the gauge being on whenever the battery is connected. (key off)

That would get me thinking about the ignition switch, BUT it would effect the other gauges too....since they all run off the same 5 volt limiter.
That only the fuel gauge would be "on" is virtually impossible.

One other thing...as far as the new fuel sender goes. Don't assume new is "good"
New just means there is a 50% chance it might work straight out the box.

[Deleted]

As far as trouble shooting.
If you remove wire from sender and ground it, the fuel gauge should peg. If it does not, the problem is elsewhere. (likely)
At that point, I would access back of cluster without fully taking it out.
Not sure how well it can be accessed from floor board....Might have to take screws out and tilt it forward at top.
(Don't forget the 2 screws that come in from behind on sides of steering column notch)
I'd check voltage in/out of the 5V limiter, which will require the key/ignition switch being in on position.
Since you say the gauge was on anytime the battery is connected, I'd check with key off also to confirm/deny that issue.
If it turns out your fuel gauge is bad, I probably have a spare I can send you...depending on which style you have.

[DynoDave]

Good points Tom. That's why you're a Master Tech, and I'm not!

I was just thinking in terms of that one symptom...because I've had it happen to me.

[Deleted]

Dave, there is no doubt that bad 5V limiters fry gauges in our old Mopars. So, your info is still good.
And if I had a bad gauge..... I'd replace the gauge and update the limiter with a modern one.

[Nacho-RT74]

Rallye or standard cluster?