76 F150.
Is there a ground wire in the connector to the cluster? If so can someone tell me which it is?
Am having intermittent gauge issues (temperature and oil pressure as well as fuel gauge). New fuel and temperature sensors as well. I'm guessing I'm having grounding issues but have no idea which wire is ground. Thanks in advance for any help

 

Electrical gremlins are fun!

Not really...lol.

There could be many reasons for the issues that you're experiencing now. You'll have to "drill down" the list of possibilities, eliminate them one by one. I can try to help you.

You say that your temp, oil, and fuel gauges are intermittenly working. I'd start with the simplest thing and work your way down.

Are the wired connections at the sending units attached correctly, clean and tight?
Any damage to the wires along the way?

Have you removed the instrument cluster? If so, have you verified the condition of the printed circuit board? Sometimes those go bad over the years, connections get corroded.

Have you verified that the gauges are connected to the printed circuit board, maintaining a solid electrical connection?

It could possibly be the "IVR" the instrument voltage regulator that needs replacement..those go bad over the years and will cause your gauges to go "wonky".

Do you have any electrical testing equipment such as a multimeter, and or a circuit test light? You may need those tools to test circuits. resistance, etc.

Do you have any manuals to reference so you can look over the wiring diagrams?

 

ditto what blackjack said. I had mine do that and I removed the I/p and cleaned the plug in connector with a pencil eraser on the I/p side and the connector side- problem solved.

 

Yes there is a ground wire, but what are "intermittent gauge issues?" What's the actual problem? What do you expect them to read, and what do they actually read? Do all three exhibit the same behavior, or does each malfunction in its own way? If so, how does each one malfunction?

 

Finally got back to a computer that I can type on.

Background - when I stated frame off I mean frame off. As part of this, the entire wiring harnesses were replaced with a painless kit, properly (i.e. all connections soldered, properly insulated and tested) installed by an automotive electrician. This certainly doesn't mean a mistake or two may not have been made as these things can happen.

I'll try to answer the questions, but I'm not sure I have too much more to go on. The truck is in Washington, and I'm in Arizona, so this is the best description I can come up with (hence asking if there was a known ground wire (or wires) from the cluster).
The coolant gauge does not rise to indicate the engine is coming to normal operating temperature. The wire was tested for continuity and tested fine. The sending unit was then replaced and the same result (i.e. no change from the "C" to the mid portion of the gauge).
The oil pressure gauge works when it wants to. Work meaning reflects what one would expect the normal oil pressure to be (mid to high).
The Fuel gauge stays at 1/4 tank and does not change regardless of the amount of fuel in the tank. This is a new tank and new sending unit, and the wire to the gauge has continuity.
In short, all gauges appear now to be flaky at best, and non-op at worst. They all (except the fuel gauge) worked "nominally" a few days ago.

I will be there to see the truck in person tomorrow afternoon, and can do more specific tests then. The plan is for me to drive the truck back to AZ. Wish me luck : )

Speaking of tests, a new temperature gauge (aftermarket) was connected to a new wire from the sending unit. The new gauge reflected similarly to the old original gauge. Not being there makes it tough, and I'm unsure if the test was valid, or if there is a a better way to test the sending unit.



Sorry to be vague with the answers/descriptions. Probably not nearly specific enough to chase electrical issues.

Thanks for any further ideas.

 

Got it. So all three behave differently. The first thing to try is to turn the key to accessory, then ground each sending unit wire (one at a time) and watch for the corresponding gauge to peg all the way to the right. Report your results.

The factory gauges are powered by a 5-volt RMS switching regulator (called an ICVR), which itself is powered from the accessory bus through an 8.5-ohm resistor wire. Was all of this retained in the restoration?

If you disconnect each sending unit and connect a test light between the sending unit lead and ground, you should see the light blink approximately once per second, which is the ICVR output. The exception is if you've replaced the ICVR with a modern electronic replacement. These don't have tuning ***** (more information here: https://www.ford-trucks.com/forums/1...-the-icvr.html).

 

I finally got in touch with Pop again and he thinks he's fixed the issue. He replaced both the fuel and temperature gauges within the cluster and they now both work. Evidently the oil pressure gauge is working now as well for magical reasons.

I'll have a chance to look at it hopefully tomorrow. I have a feeling we're not quite out of the woods yet.

FMC400 - he mentioned that he notices now a faint "pulsing movement" of the wiper blades when the truck is running that he hadn't noticed before. He states it looks like they're trying to turn on.
Any ideas? He's since pulled the related fuse.

One other thing he mentioned (wish he'd have mentioned this earlier) that the turn signals blew a fuse. This was shortly after the gauges starting acting up.

He's replaced it and they are working fine at this time. Unknown if it's related but didn't want to leave out that detail.

Thanks for your help and any other thoughts you and others may have.

 

Glad to hear the gauges are on the up and up.

The movement of the wiper blades could be an intermittent short in the dash switch, or the park switch (which is in the wiper motor itself). It's a little tough to isolate, but my first guess would be the dash switch - if it has a short, it may try to turn the wipers on, but the park switch in the wiper motor may return them to park. The dash switch is also more susceptible to wear, since the park switch in the motor is typically heavily lubricated. My wiper switch is worn enough that it has a hair trigger; I barely have to touch it for the wipers to turn on.

My computer is taking a really long time to load, so I'm having trouble pulling up the wiring diagram. But on earlier trucks, the turn signals and wipers shared the same fuse, then later they split. If your '76 has a dedicated turn signal fuse, then whatever caused that fuse to blow is likely unrelated to the wiper issue. But you'll want to keep an eye on the turn signal fuse and ensure that it was replaced with the proper amperage as labeled on the fuse panel. Fuses do get old, so the fact that it blew doesn't necessarily mean it will happen again.