The car isnt grounded I believe. Check if you have some unplugged cables in the engine bay. Quite likely will be some coroded contact, all what you need to do is clean the contacts and ground it again
Aint funny tbh, had something similar years ago back home on my e36 bm.
The last owner took the subwoofer with him and left cables under the boot mat unsecured/bald, the mat caught fire with the spare wheel whilst driving luckily i had a big bottle of sprite in the car at the time helped very much