Hi Borko,

Find the Volvo Greenbook wiring manual TP3932202 for your car.
I don't have it here. I found the manual # you want, now you find the manual.

I spent 18 months finding the right book for my 1994 945T. It suddenly
showed up at Ebay. I never found it on-line, but did find plenty of crappy
Google proxy sites that offered unknown manuals for $$$.
You're sunk fixing wiring issues without TP3932202. There's a lot of
manuals for free on-line, but the sleazy search engine monopoly wants to
send you to their proxy sites for $$$. Give a try, get lucky and surprise everyone by posting back with a valid link to the manual. Maybe someone
can chime in with a good link?

In the meantime I'd suggest that you service the battery terminals.
Including taking all the piggyback wires off the positive terminal,
shining them up with a small wire brush and reinstall using conductive grease such as copper anti seize or Penetrox-A.

Loose battery connections might cause that problem.

If that doesn't work provide a link to your manual and I'll try to help you.

Post back with what you do to solve the problem.

Good luck, Bill