But I also know that sometimes the tails get moisture in them and the sockets and/or bulbs get corroded.  That would trigger a code.  Take the bulbs out from inside the trunk and take a look.  If these parts need replacement, buy them at the dealer, where you get real brass; the parts store parts are junk.

Another common issue in the trunk of an E36 is fraying of the insulation on the wiring harness that is routed along the hinge on the driver's side.  Opening and closing the trunk over the years causes the wires to chafe.  You'll need to unwrap the bundle, carefully, and pull the wires apart to see if there is any damage to the individual wires.  This problem might also be responsible for the trunk lock problem you have, as the power lock wiring is in that bundle.  Splicing in a new piece of  wire is easy as pie - just be sure use a watertight seal like the shrink tubes they sell at Radio Shack.

When Mike is back, he'll probably straighten you, and me, out...