Can’t get these gauges to work…

Hi there!
I’m new here…
Just picked up a CLEAN 60,000mi 1990 GMC Suburban 3/4 R2500, 2wd with a 350tbi and a turbo400.
Getting a few gremlins sorted, but I can’t for the life of me figure out what’s going on with my fuel gauge, oil pressure gauge, and temp gauge.
I started out with the usual, swapped in a new oil pressure sensor, new temp sensors (both), and a new fuel pump with sending unit.
The fuel pump was weak anyway…

My speedo (the electric one) works as it should, and my volt gauge works as it should.
Oil pressure moves up just a tad when I start the car, but then stays there (around 10psi) regardless of engine speed/throttle input.
The temp gauge does the same… moves up just a tad when engine gets hot, but stays at maybe 130 at operating temp.
Fuel gauge was kinda sorta working before I changed the pump and sending unit, and it would show like 1/3 when tank was full, and 1/8 when tank was empty.
Now with the new sending unit it goes up when I shut off the car, and drops instantly to empty when I turn on the ignition.

To me there’s gotta be a relation between these three gauges not working… ?

I’ve removed the gauge cluster and had it apart with the gauges out and cleaned everything. The circuit board has no obvious cracks or anything to it, and the terminals look OK.. maybe not super clean, but not awful.

I thought maybe it could be a grounding issue, and I also went ahead and removed and cleaned the little ground “tree” terminal that’s on the dash “wall” on the inside of the dash to the left of the gauge cluster.
That did nothing.

I’m not great a diagnosing electrical stuff, and I don’t know how these gauges & sending units are routed from the sensors etc up to the gauges, but I do have a multimeter, and if someone tells me what to measure etc I can try to figure it out.

I’m tempted to just pick up a used gauge cluster I just found online, but then again if that’s not the problem, I don’t wanna waste the money.

To me it seems like all the gauges with 3 inputs, meaning not just positive and negative like on the volt gauge, are not working. (Excluding the speedo which works).
The main wire connections seems ok too…

Any help would be massively appreciated.
I’ll attach a pic of where the gauges are at when the car is running.

Thank you!

I'm not going to be of much help, but maybe some. unfortunately you have already tried most of what I would have suggested.

The easy one is the fuel gauge. It's very likely a bad gauge. If you get a new gauge be sure to get the resistor for it, if you get a used gauge buy a new resistor. if you disconnect the sending unit at the tank ground it out the gauge should go either past full or to empty, leave it disconnected and the gauge should go the opposite direction.

Oil and temp are another story. Have you check the oil pressure with a manual gauge? you sure it's warming up like it should? If yes then i would be looking at that circuit board on the back of the cluster really close. you have already checked the grounds, but clean the multi-wire plug for the cluster on both sides. Pull the gauges out of the cluster and make sure each gauges contacts are clean and tight. you could run resistance test on the wires from the sending units to the dash, and check the bulk head connector. Other than that it I'd be looking at the gauges. Really really look at that circuit board and the gauge contacts.

That's what I'd be doing anyway.

I'm kind of drawing a blank here...

Try physically moving the needles on the inactive gauges to full scale with the ignition off (they should stay in roughly the same location you put them), then turn the ignition on and see if they return to zero. That should help determine if they're receiving power, but no signal from the sender, or not.

I recall the being able to manipulate gauges with power ground on legs but I cant remember if that was ford LTD or the square.

@ohaggdahl,

Welcome to the forum from Louisiana first of all. well, I've been working with my gauges, Autometer, and studying the schematic for a couple of weeks now while I puit in a new Amp gauge and running wires for it and double checking all the wires for correct placement and whatnot. Like others have suggested here already, I would be taking a close look at the printed circuit, to.

But what I can't understand is, why all those gauges at once? I'm trying to think what do these gauges have in common that could be not working right now. and I can't see anything as far as the schematic is concerned that all those gauges would not be working because each one comes into the instrument panel from a separate place on the engine and goes to separate places on the instrument cluster. Just make sure those clips, that the pins on the back of the gauges, are making good contact with the printed circuit and that they are not loose at all.

Their contact with the pins on the back of the gauge should be tight when you push the gauge into the clip. Those clips are the only connection the gauge has with the wire that connects them onto the printed circuit, from where the gauge wires come into the dash from the fuse block down on the firewall in the cab from the engine compartment. You could be only getting partial signal because the clips are loose.

There are different senders for gauges or idiot lights, I believe???

there is a member named Hatzie on here that knows wiring inside and out.

Those three gauges share two different wires when it comes to the printed circuit board. A positive 12 volt switched ignition wire and a common ground wire. Then each one has its own sender wire. Is the voltage gauge working properly, and are the cluster illumination lights working properly? If those are working properly it is safe to assume that the grounds from the cluster are ok. The next thing to look at would be the printed circuit board. Since the issue you have seems to be three wires directly next to each other. The 3,4, and 5 wires control the three gauges you are having problems with. Makes sure that there is no corrosion or delaminating of the circuits from the plastic. If there is none, then the issue will have to be traced to the main firewall connector harness to ensure there is no chaffing of the harness or corrosion in the firewall connectors themselves.

With the ignition on, unplug the senders and see what happens. Then ground out each sender wire and see what happens. If the gauges move full swing during these tests, then the senders are faulty. If the guages still just kind of sit there, then continue looking for chafed wires to the cluster or bad spots in the printed circuit. I'd start with bench testing the cluster before tracing wires.

A lot of good advice given already,but it wouldn’t hurt to ohm out all your grounds and clean/repair as needed. Good luck.