I have a 1991 740 wagon non turbo 2.3 liter b230f engine that has no working brake lights. The fuses are fine and its not a relay issue. When you turn the foglights on, however, the brake lights come on....what could be the problem?

"...When you turn the foglights on, however, the brake lights come on..."

The rear fog lights LOOK like brake lights because they are quite bright, but are actually a different bulb seperate from the brake lights.

Hey SF1,



Have you checked the bulb out sensor? A solder joint cracks inside and you lose your brake lights. It happened to mine. Wiring ok, switch ok, bulbs good, no lights. You can open it up with some patience and re solder the joints if you're handy with an iron, or fetch a spare from a junkyard. If you want a new one, its like 100 bucks for OE and 60 or so for aftermarket. I think most Volvos had them back to 85 or before. Its a big red thing at the back of the relay panel in the fuse box.


Regards, Jon 'Uncle Olaf'

Had this happen to me too. The current for the brake lights flows into the relay on one solder path and the splits into two traces. A reed switch compares the current and if no current is flowing for one side the, the bulb out light turns on.

If the one solder trace is cracked, you have no brake lights.
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Paul NW Indiana '89 740 Turbo 140,000