The dreaded electrical Gremlins strike again!!

I absolutely HATE electrical issues, and we seem to have another one. My
partner flew from Indianapolis to Dallas (via Oklahoma City) and back
over the weekend. Everything was fine on the way there. On the way back
he started having avionics probems. It started with the VOR needles
twitching and then the 430, fuel totalizer and finally the comms went
inop. He noticed that the landing light would not stay on, like there
was a short somewhere. We had an issue with the landing light wire
shorting out before causing the breaker to not reset. This was fixed
last year.
He was able to make it back to Indianapolis with no issues as long as he
went 2600 rpm and 25 MP. This power MP setting is seems did not cause
the issue to occur. When he throttled back to say 2400 squared the
problem manifested itself again.

So I guess my questions are these:
Could a short circuit in the Landing Light circuit cause anything that I
described?
Has anyone here had an issue like this before? And last but certainly
not least do you have any suggestions?

Thanks!!

Jon Kraus
'79 Mooney 201
4443H @ TYQ