GM-GMC: GMC Brake Light Problem, gmc savanna, tail lights

Question
I have a 2001 GMC Savanna Van.  When I use the tails lights and brake lights separately. They work fine. When I have the tail lights on and step on the brake pedal, my rear right brake light goes out.  Any suggestions?

Answer
I am going to guess that you have a problem with the pigtail assembly.  If my memory serves me right, there are three sockets all on one assembly, one of the sockets has a contact problem and it plays tricks with the rest.  I would try swapping the assemblies from one side to the other, if the problem moves, replace it.
Quick and easy way to narrow the cause down.\
Hope this helps