Intermittent gauge operation
 

Well I think I'm wording that right. Basically my problem is that half my gauges are off in one way or another. Speedo is off by 5mph, tach seems fine, oil pressure seems fine, gas is off by 1/4 and temp is off by 1/4. The only ones that bother me are the temps and my gas and it will be correct and wrong intermittently so I'm wondering whats up with that. I used to think it was seasonal but not so sure, sometimes it'll go months being wrong and sometimes it'll go a couple days. Anyone else have this problem? Anyone know what might fix it?

Speedo being off could be the tire size or could be speedo age, but 5 mph is within the factory
limits so I wouldn't complain.

Gas off by 1/4 usually means it never registers full even when full. If thats the case you need
to clean up the connectors on the tank for the fuel sending unit. The guage is based on the
resistance level and corrosion increases it over time. If cleaning it doesn't work, you can fix
it usually by providing a good ground from the tank to the mounting tab on the sending unit.
I did this by running a small wire from one of the sending unit bolts and tapping a small hole
in the sending unit mounting tab for the sender connection and attaching it there. Otherwise
you will need to remove the sender, and that can be a bitch because of the bolts getting
frozen and snapping off.

The temp being off may be a corroded attachement, its under the oil filter or it could be the
cooling system is not up to snuff. I had mild heating issues with a clean radiator, new hoses,
cap and flush until I replaced my oil cooler hoses. If you have a beehive, they suck and don't
cool very well.

Well the thing with the temp and fuel is that they are connected by something. By that I mean that when one gauge goes off by 1/4 so does the other. This isn't the first time this has happened, maybe the 8th since I got the car. Basically it does it every few months and it'll happen while I'm driving. I'll just happen to look down and I'll either watch the gauges drop or I'll look down and say oh hey I'm at a half a tank and I just filled up... and it's running between 100 - 120 degrees. I just can't figure out what is common between the 2 that would make both of them give a false reading, just can't seem to figure it out from wiring diagrams.

Theres is a ground for the dash up under and behind the console with the guages
in it. Its a black wire that comes out of the loom by the fuses and attaches with
a philips screw into the metal of the dash. Its a bitch to see, you have to be upside
down in the footwell looking straight up at the bottom of the dash using a
flashlight. Make sures its tight or retightened.

Both those guages are based on resistance and your description is telling me
that the resistance goes up occasionally while driving.

You might want to check the other grounds as well. These one on the driver
shock tower and one in the rear from the muffler to the muffler bracket bolt.
There may be another but I can't recall, those are the common ones.

I thought the one by the muffler was a safety cable in case the rubber muffler mounts broke.

I'll check those grounds. I was unaware that they were resistance based so I'll have to give all that a good go through and cleaning. They're probably just corroded after 30 years so hopefully they just need a good cleaning agent and a solid scrubbing. Thanks again!

Your symptoms can also be caused by low voltage. If your charging system allows the voltage to drop it will affect the guages in unison. Also if you have to many electrical components wired into the ignition circuit that the guages work off of then when they come on (like an electric fan) then it can also cause the guages to be affected.

Good to know. I've got my e-fan wired up to the fc fuse box that I installed with a 40 amp fuse since that was what was in the box when I got it. Aside from that I have an fc alternator and a 400 watt 4ch amp. I'll keep it in mind as it didn't stop raining till late tonight, hopefully tomorrow will be dry so I can give the whole thing a look over.

Watch the gauges with everything turned off and then turn everything on and see if they move. If they do so in a similar way as what you have seen them do in the past you will know thats your problem.

Ok I'm stumped. I feel like I've looked every where under the dash and can't find the grounding point. Can anyone draw me an arrow on a picture to where its at?

Get in there upside down with your head against the brake pedal and looks almost straight up.