Hey everyone, Im trying to get an idea of what might be going on with my gauge cluster. I pulled the cluster out to replace my headlight/dimmer switch and also took the opportunity to install some LED bulbs in the cluster. Today when I was putting the cluster back in I wanted to test everything before I put the dash back together all of the way, my gauges were working but only my left turn signal indicator would light up and my brake warning light would light up. None of my other instrument cluster lights would work. After fooling with it a few times I decided to bench test the cluster just to make sure it wasn't the bulbs not being compatible and to make sure there were no problems with the wiring on the cluster itself. The bench test was a success so I went back to the car and tried to install the cluster again and still only the left turn signal and brake warning light were on(cause parking brake set). After loosening the two 10mm nuts at the bottom of the cluster I decided to moved the cluster in and out slightly and the rest of my cluster lights would flicker. I looked and tried testing the connectors and everything was checking out fine. After about 4 hours of troubleshooting I decided to give it a break for now and thought id post it up here to see if anyone else has had this problem and some ideas oof what I should do/try. It is a tight fit and the connectors don't pull out far enough to plug them in to the cluster outside of the housing to test maybe a loose fit, so I was thinking about cutting and extending the connector wires to work with it outside of the housing to get a better idea of the problem. Any help is appreciated.

 

Hey man, I have an 85 IROC too, and just happen to be doing the same chore as you.

I noticed the same flickering when trying to test gauge and light functions. In my case, once I secured the cluster in place, including putting on the outer black trim piece, the dash lights worked as expected.

How did you bench test? I am good mechanically, but my electrics experience is nearly nonexistent.

As I said, most of the dash lights are working, but the fuel gauge, temp gauge, and tach all are not working. The gauges that are working are the speedometer, voltage and oil pressure.

I’ve had the whole cluster out, and I removed most of the metal gauge clips and cleaned them. That did seem to help, but didn’t affect the gauges.

I’m wondering if my printed circuit board is bad....

How can I check that I’m at least getting a signal from the fuel sending unit to the dash?

 

I bench tested mine by tracing the wires in the printed circuit and finding the constant power and ground to make sure my lights were working. My gauges worked when plugged in. To check for signal you'd have to figure out what wire is for the fuel sender and see if you have power there. Is your fuel gauge just stuck in a certain position? Thats what was wrong with my gauge but figured out the the fuel sender was bad and replaced it now it works like it should.

 

It doesn't exactly "send a signal".

The sending unit is just a variable resistor with one end grounded. Looking into it from the dash connector, you'll see a low resistance (below 10 ohms or so) when empty, and something near 100 ohms when full.

The gas gauge itself has 2 coils: one has 12V across it at all times that the key is on, and that coil makes the pointer go toward Full. The other coil has 12 volts on one end and the variable resistor on the other, and tries to pull the pointer toward Empty. The change in the sending unit resistance as the fuel level changes, changes the current in the coil that moves it toward Empty. The location that the pointer stabilizes at is thus a balance between the 2.