v70 l electronic problem

Hello dear community, I’m new to talk and new to volvo. Consequences of the problem I have: I bought myself a volvo v70 10v automatic gasoline from 1998 with 213,000 km. The vehicle ran ahead, and a week after the purchase quite normal, then after I had a defective glare lamp and an electric wheelchair crane, including wiring, which was developed by the previous owner, appeared on the journey afterwards a very illogical problem for me. the light switched off, and a “loud” relay was to be heard, the car only jumped on again when I turned the light switch to 0 position. Then in the engine room it smelled a bit like unburnt petrol. The car also now only runs when the light switch stands at 0, as soon as I press a flasher, the light or a window lifter the car goes off and this loud relay (I found out it is the light relay) is to be heard with 3 circuits, just like it is who n I only turn on the ignition without starting the engine, then activate the light switch. In addition, the windscreen wiper moves whenever the problem arises. I suspect a mass error, however, don’t know how to find it if it is one and doubt if it makes sense to have a workshop measured for hours. Of course, it is my problem, but in addition, that the car in Switzerland is at my temporary workplace and will still be transferred to DE. would like to. I would exclude the lima, because the symptomatic is there even with not running motor. Does any of you know such a problem? Rejoice me about every answer/help/tip. Thank you in advance. Greeting tobi