Volvo 850 T5R electrical failure?

Moin, I have a few questions, I have been able to buy a T5R quite cheaply, but logically not 100% running. The beautiful has a problem, the motor starts only rarely. Sometimes only once a day, sometimes not. I have already researched and worked a little bit, bridged the WFS, with which he then also ran so far that I could drive him into the workshop. Furthermore, I noticed that he only sometimes sparks and when then he usually starts. That’s why I think it’s a mistake somewhere in electrical engineering. The previous owners had a gas system from landi renzo (I think:P) installed and the workshop that did this also broke the relay box into 3 pieces, so that the relays met me 0_0( still in their plug in) I have ordered a new relay box that I then want to install, someone still has any ideas that I can best look at in the cable salad or what other reasons could there be? I have already thought about the camshaft sensor? Thanks for all the tips and for the help!