1987 Chev R20 PU - 5.7L Fuel Gauge

[Tim Martin]

I got an 87 R20 Chevy pk tk with a 5.7/auto trans 2wd.

Issue is the fuel gauge, oil pressure gauge do not work. My question is: According to a Mitchell wiring daigram, they have a common power supply connection from the gauge/idle fuse. Should I have 12 volts on the power supply terminal of the gauge? Or is there a buffer or something to lower the voltage. The issue is that koeo the gauges go to past the full mark or past the right side of the gauge needle sweep. Grounds are excellent. I took them apart to make sure. I even ran a new wire from the fuel sender thinking that there may have been a short to ground or something. After a week of on and off with this thing I am next to pulling my hair out.

What am I missing?

[steven kiser]

it's been a while but i think if i recall correctly you'll find a cracked or ripped circuit panel. check where the harness clips into the back of the cluster for any flash marks. i think that you're loosing ground intermittently.

[Tim Martin]

Well steve, I have taken the dash out and laid on my office desk for diagnosis under a magnifying glass and found nothing. I ohms checked the ground circuits and found that to be good also. I am just not sure where to turn.

[steven kiser]

i've had issues with the wire where it attaches to the connector that's part of the plug that plugs into the back of the dash. now i'm confused..........

[Tim Martin]

I did some more diagnosis and found that I have no continuity between the terminal where the wiring harness plugs in the back of the instrument cluster and the terminal feed for the gauge. So I am forced to conclude that there is an open on this circuit on the printed circuit board even though I cannot see it. Now for trying to locate one a these, new or used.

[liljoe]

In cases like this, I have been known to soilder a jumper wire from the board near where the plug plugs in to a point somewhere else that is supposed to but does not have power. These are fairly robust printed cuircuts and are not that bea to soilder to......

[Tim Martin]

Do these gauges operate on 12 volts? Or is there a voltage reducer somewhere between the ignition switch and the circuit board?

[steven kiser]

i don's see one in the wiring diagram but i'm thinking that the 12 volts is there but it's working on low amps. for some reason i think there is a wire type resistor in the harness.

[Tim Martin]

Well I am thinking the same. Is there any way to find this out? The guys at the dealer are not familiar with these systems. At least that's what they say.

[steven kiser]

if it were me i would spend a bit of time googling it or look for an old time g.m tech. when i get a chance i'll drag out my wiring books from yester year and see if it has anything that will help. it may be tomorrom a.m.