I bought my 86 240gl a good 2 months ago and i'm loving it so far...but when i first got it i noticed the gas gauge would work once in a great while and the temp didnt even work. It was weird, when the gas gauge used to work i would look at it --say when i got on the highway and once i got the car to speed, i would look again and the needle would say the tank was empty.

Now the gas gauge doesn't work at all, but the temp gauge will do what the gas was doing when i first got the car.

My self diagnosis on this is just some bad wiring back their due to the hack job someone did back there while bypassing the inner amp for the speakers.

Can anyone else that has had this happen to them help me out on this?

Bump.

This could be a lot of different things.

If your temp gauge needle is at the very bottom and you hit the dash and it jumps up where it should be, its probably a bad connection on the temp comp board on the back of the cluster. Or the temp comp board is bad - a common failure. Or it could be simple like one of the wire connectors on the back of the cluster is loose.

Clean fuse #13.

For the sedan a removal of the trunk carpet and metal inspection plate will allow you to inspect the grey wire used for the fuel sender.

One thing that both gauges have in common is they are supplied +10V from a 3-pin voltage (socketed) regulator on the back - you would need to measure its output with a meter to know if it’s the problem.