I have a 2002 VW diesel bug and have had problems before and fixed them, but just rececently (all within a week and a half) have had all kinds of completely different problems.
FIRST, the speedometer just quit working while driving down interstate. A day later the air conditioner stopped blowing cold. But the ac was an off and on again thing. So I changed the fuse box on top of the battery because one of the 30amp fuses was not blowing but the holder was melting. I also changed the transmission speed sensor.
THE fuse box works fine but evidently the speed sensor on the top of the transmission was not the problem.
I disconnected the speed sensor again and turned the inside square pole and the speedometer jumped, so i dont think the wires running to it are bad either.
NEXT, trying to make the ac work, I checked the freon, which appeared low from the gauges, but the system would not take any freon. I then wired the compressor straight to a 12v battery which assisted it in staying on (because it would kick on and off continuously) but it still did not blow cold.
ANOTHER problem is the brake code came on on the dash. So i checked the brake fluid, and it was fine.
THAT very same day i checked the brake fluid, the temperature gauge up top by the clock stopped working. And i have changed that sensor about two years ago.
I think it might be wiring or a short somewhere but i dont even really know where to start or what to start looking for, it all looks pretty normal.
I checked the ground wire on the battery and it has a little corrosion but i dont think enough to do anything.

PLEASE if anyone has any ideas of why this is all happening so close together, please share them, anything to try will help.

 

Get a new battery even if it tests good. That is the only thing I can think of that would cause all those things in that time span.