Yep, Cletis is right. I have a multimeter too and sometimes it works better for certain situations. The important thing to do is to find the problem and fix it right the first time instead of running to the parts store every hour ending up replacing the whole thing before you find the problem. It may be that you just have a bad ground, both of my parking lights didn't work until I cleaned up the wires and ground location. Although I think it is extremely rare, it may be that the filaments to the brake lights on both sides are burnt up but the tail light filaments are still good.
