Radio electrical woes

[Bathtub57]

The radio in my 912 is a horrible 90's Pioneer headset which works fine except when I brake or indicate it cuts out. I'll replace it down the line but for now it would be great to get it working properly.

I'm guessing it was set up correctly at some point in time so thinking it's something to do with an earth? But where do I start?

Appreciate any clues.

Cheers

Mark