Gauges

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Jgriggs

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Location
Spokane
First Name
Jim
Truck Year
79
Truck Model
C30
Engine Size
454
Instrument cluster seems to have quite working.
Volts, oil press. Clock, temp, and fuel Gauge.

Clock has never worked since I've had the truck. 79 C30 btw. Maybe the clock is relevant to the problem, maybe not.
The rest of them did work. The temp had been reading about a little above the midway point, but had started reading cold, like about a needle width off the C line however heater was still blowing hot, coolant level good.

Oil pressure is pegged all the way past 60 psi, does not drop when key off. I had a 91 camaro that did this too, that was because the sender was not plugged in. In this case it is.

Fuel, we'll at 8.5 mpg, it might well be working I guess, it stays at 1/16 all the time. There is a gray wire coming out of the back of the fuel Guage, that wire is not attached to anything, it was broken. There was another gray wire in a loom that was also broken, that wire being about one size smaller. The only gray wire I can seem to find looking at diagrams is a speaker ground. Neither of these two wires have power going to them either with key on or otherwise. When I check them both for continuity, they both have continuity to ground. Put them together, and still nothing.

I don't care what time it is, volts, oil pressure, and temp would be nice, but not super important. But gas at 8.5 mpg...yeah, I need that one.

Any ideas?
 

75gmck25

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Northern Virginia
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Bruce
Truck Year
1975
Truck Model
K25 Camper Special TH350 NP203
Engine Size
5.7
There is a black instrument panel ground wire that connects to a post on the top of the emergency brake mechanism. All the other instrument wiring for the non-tach instrument panel is usually through the large multi-wire plug that plugs into the back of the panel. I would bet on the ground wire as most likely issue, but that large plug may have also vibrated loose.

I don't know what the gray wire is that you see on the fuel gauge, but on my '75 truck the gray wires run to the panel bulbs for illumination. My fuel gauge makes all the instrument connections through the two posts on the back of the gauge. If your fuel gauge is the standard large diameter unit, it also has a brake warning light integrated with it.

In '79 I think the sending unit wire is tan colored. If you have only one tank it has a pop-apart junction at the frame rail near the tank, and from that junction the wire runs up the frame rail to go through the firewall near the brake booster and enter the instrument panel wiring on the other side. The section of wire that comes up from the frame rail and across the back of the engine compartment is subject to damage when you are doing other work on the engine. It may even run close enough to the exhaust to have been burned through.

If you have dual tanks the sending unit wiring gets much more complicated and there is a tan wire for the primary tank sending unit and a tan/white stripe wire for the other tank.

Bruce
 

Jgriggs

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Joined
Nov 2, 2016
Posts
10
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Location
Spokane
First Name
Jim
Truck Year
79
Truck Model
C30
Engine Size
454
It was the ground. I figured it must have been, but the gray wire had me thrown off. That may well be the light for the fuel. I honestly can't remember if that one works or not. Too bright outside to check without pulling it all apart and looking at the bulb.
What I can say about this truck is that the electrical is a soup sandwich. Picked it up this past summer for free, and parked it. Now I'm trying to exorcise the gremlins. But oh how they are not happy about. Everything I fix flushes out two more.

Fuel gauge works.

Excite wire to starter kaput. . .somewhere
Brake line leaking at right rear.
 

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