1989 grand marquis
Well my headlights work and break lights it's just
my tail lights not coming at all I check fuse but
can't find out problem I switch the bulb
Do the park lamps in the front work? I they do, I don't think the problem is a fuse or switch, I think it a wiring problem. If none of the lamps work, then you will have to check everything, Use a test light and check voltage on fuses. Check voltage and ground at the rear, hopefully the brown wire is voltage and black wire is ground. You might be able to use jumper wire on correct wire colors and bypass the headlamp switch. If the lamps work with jumper, the head lamp switch has a problem. Just my opinion.
