Gauges & electrical

[bmiszuk]

Since I put the engine back together, I have a few electrical problems. These things aren't working: voltmeter, oil pressure gauge, high idle and IP cold advance.

Anyone have an electrical diagram that might help? I did remember to reconnect the ground connection at the back of the passenger side head. I thought maybe I missed another ground or connector somewhere but I sure can't find it.

[bmiszuk]

Anybody? Any suggestions?

[Robyn]

These issues are very likely tied to a common power feed thats been either unhooked or broken ????

The feed for the volt meter is likely a common power feed that comes from the ignition.

The Cold advance/fast idle feed through a temp switch at the RH rear of the RH head.
Make sure this is plugged in and that the switch is closed when the engine is cold.


Now it is possible that you have a fusible link at the starter +++ post thats failed.

Anything that feeds the instruments could do it.

The Oil pressure and the volt meter are both electric gauges.

This really has to be a common denominator.

Something that was unhooked during your work under the hood.

Robyn

[bmiszuk]

Thanks Robin.

I found the temp switch at the back of the right head and it's broken. One of the terminals is missing. Replacing that should fix the cold advance/high idle problem.

We're still stripping back the wiring harness to fix the oil pressure/voltmeter problem.

[bmiszuk]

I found the problem. Of all places, it's in the dash! The little clips that the gauges snap into aren't making good contact with the PCB.

My son and I tore the entire wiring harness apart under the hood. Found a few interesting surprised and messes. Some electric tape and cable ties cleaned everything up.

It's funny. All the gauges worked before I parked the truck a couple years ago. Evidently while it sat, the connections got corroded or loose or whatever. The little clips are loose and there is corrosion behind them.

Well, at least we know what the problem is.

[Robyn]

Sitting is tough on stuff, especially if the weather is damp.

Glad you found the problem.

Once you get a good temp switch in the RH head, things should work fine.


Robyn

[tomtaylor]

I am in the middle of doing several electrical fixes on my 86 GMC and would also like a little input on a couple of items if anyone knows these answers here.

1. is the voltage at my fuel tank sending unit power wire supposed to be 12 volts? I finally got the sending units to work after giving them a good ground but I am only getting 8.5 volts on my meter for both units and I am also getting 8.5 volts at the dash fuel gauge?

2. when I ordered new senders from rock auto they came with 3 tubes and mine only have 2 tubes, what are the extra tubes for, vents? the new senders also show a higher ohms resistance in full and empty positions than the old units so I think they are showing my gauge as not quite empty and a little over full. if they sent me senders for the wrong year would they really be that much different.

Thanks
Thomas

[tomtaylor]

I am in the middle of doing several electrical fixes on my 86 GMC and would also like a little input on a couple of items if anyone knows these answers here.
1. is the voltage at my fuel tank sending unit power wire supposed to be 12 volts? I finally got the sending units to work after giving them a good ground but I am only getting 8.5 volts on my meter for both units and I am also getting 8.5 volts at the dash fuel gauge?
2. when I ordered new senders from rock auto they came with 3 tubes and mine only have 2 tubes, what are the extra tubes for, vents? the new senders also show a higher ohms resistance in full and empty positions than the old units so I think they are showing my gauge as not quite empty and a little over full. if they sent me senders for the wrong year would they really be that much different.

Thanks to anyone reading my message above but I just answered my own questions.