65 Belvedere gauge issue

[65BLVDR2]

I went through some of the posts regarding the fuel gauge not working properly for various models, and saw on one that said that the fuel gauge and temperature gauge are tied together. So usually if one goes both goes. My temperature gauge works fine, the fuel gauge does not. Also the speedo and odo are not functioning. Previous owner stated the speedo and odo were working, then one day the speedo jumped up to well over the actual speed, and the odometer followed suit. Now neither function. Any ideas? I'm pretty decent with elecrical work and am good with a soldering iron, just was curious where I should look first. Thanks.

Also the alternator gauge works fine as well.

 

[Badvert65]

Fuel and temp are only connected by using the same voltage regulator. Electrically, they are separate devices. My experience has been that most fuel gauge problems start at the tank. Either faulty wire, connection, ground, etc. Or, as in my Belvedere's case, the sender is bad.
Speedo is strictly mechanical, start by checking/replacing the cable.