I have the famous no light problem with my instruments and switch lights when the headlights are on. Originally I was going to bypass the rheostat / brightness adjuster, but there is a short of some kind causing it to peg the temperature and fuel gauge when I do this. There has also been some sort of halved ass repair. At some point someone installed a ground wire from the back of the instrument cluster to the negative ground post directly behind the insulation where the oil pressure hose comes through.

This problem would be easier to fix if I knew what the wires on the round plug installed into the rear of the instrument cluster went to.