My voltage gauge will work for about a month, but then it looks like this for a month or so, then back to working. Any ideas what the problem could be? Thanks.

 

Looks like a dead short. Pull the gauge and test it. If it tests OK, start looking for chaffed wires.

 

Man, your car is full of problems.hard to keep up with all your post.
Cant say ive seen that before, but I would guess its wiring or the gauge.

 

The voltage gauge is known for getting faulty. I had to replace mine and all is good. I removed the gauge from my dash and installed an analog meter. The needle on the meter didn't move like the needle on the gauge, so I determined that the gauge was the issue.

 

Did you install a speaker with a big or powerful magnet by any chance?