Instrument cluster problem

[billabx]

I have a 85 ½ 944 with a rather unusual problem. Recently when I started the car I noticed the oil pressure warning light was on and the oil pressure was reading zero. Since the hydraulic lifters were not making a racket as they would if the oil pressure were actually zero, I assumed the likely culprit was the oil pressure transmitter. I replaced the switch and was disappointed to see it hadn’t solved the problem. At this point I also noticed that the brake pad and brake fluid lights were on. Since the brakes were just replaced and the fluid is all right, I’m thinking there must be an indication problem. I’ve checked for loose or damaged wires and haven’t found anything. On my wiring diagrams, about the only thing I can find with these three systems in common is the central (master) warning light. There are a number of diodes which allow the master warning to illuminate with another warning light. I’m thinking that maybe one of these diodes has failed allowing current to leak from one system to another. Unfortunately, I don’t have any information on the diodes themselves, so even if I can isolate a bad one, I won’t know what to replace it with. Has anyone had a similar experience or managed to find a replacement for the diodes?

[Brando]

Did you clean the grounds?

[SoCal Driver]

There is a significant number of discrete components on the back of the later instruments. I would contact a qualified speedo shop and see if they or some one they recommend can fix it. But as Brando asked you need to check the ground clusters on the body. Also removing and reattaching the connectors can clear up any possible corrosion.

[toolboy62]

I have most of the working bits of a late gauge panel if that will help. Unfortunately I will be using the oil pressure gauge itself as the one in my car right now has lost its damping and the needle "flutters." I should have swapped it months ago but I keep having more important stuff to do.

nate

[SoCal Driver]

What makes you think it the gauge that is bad?

[billabx]

Thanks for all the replies.
I've cleaned the grounds under the dash and at the back of the engine. No help.
The reason I'm inclined to think the diodes are at fault is that the master warning light (which is connected to the other warning lights through the diodes) seems to be the only common point for the three circuits affected. I'm going have to put it aside for a few days, and will do some more troubleshooting when I get back to it.

[SoCal Driver]

Guess I should have prefaced my question with "toolboy62".

[toolboy62]

I remember noticing when I swapped stuff around (this was part of my whole "get the odo working and the dash lights too" gauge panel fest) that the needle on the oil pressure gauge moved really easily if I touched it with my finger compared to the other gauges. Sure enough when I swapped in the gauge panel I was working on, it fluttered and it didn't before. Taking apart the other panel revealed that the oil pressure gauge in that one is damped just like the other gauges. So it *is* the gauge. No oil pressure anomalies, it just wiggles a bit on quick pressure changes like revving when cold etc.

nate