1985 bmw 535i

Usually, this is indicative of the wires being broken (or corroded) between point a and b. On my 735 (same year), I have a running light in the rear that won't turn on. We've traced it to either a grounding problem or a broken wire. You've really only got two choices: trace the wiring from point a to b and try and ohm it out to see if there is an open or run a new wire.

you need to take a look at the light sockets in the trunk area.there are NO wires going to the lights like most cars of the time.if you take a close look,you will see that the whole panel where the lights plug in IS the wiring complete with ground.you juat need to unplug each one and scratch all the corrosion off the fixed panel AND the flat prong like connections on the bulb sockets themselves.

every 5 series i have gotten into after being parked for awile had this problem.absolutely no rear lights.and yes,check out the fuse box,but it is most likely this or-

the brake pedal on these cars has a thin plate which the brake light switch/andclutch switch is bolted to.i have also seen in many cases the pedal travelbeing too excessive causing the thin plate to bend slightly causing it not to make contact with the switch,which also won't make the brake light warning lamp come on.but i bet you its those sockets in the trunk.cause if the hot side of one is grounding out-then none of them will work!good luck.