Brake light problems

[rkjmb5]

I have a 1990 Volvo 760. The center brake light works but the other 2 do not. I checked the sockets with a tester and have juice there. I have also swapped bulbs and know they are good. Today I switched the left and right light assemblies and the brake lights worked but the fog lights quit. I have also changed the light relay block that is in the trunk with a used one. Can someone give me a hint on what the problem is.

I did not receive any replys but this is what I found out. I have 2 Volvos in my yard right now and both of them have the wrong bulbs in for brake lights. Many auto stores will give you bulb # 1156. That is not the correct bulb. The wattage ect is okay but the nubs are placed wrong. They will fit and sometimes work. I also thoroughly cleaned the sockets with steel wool and coated them with dielectric grease. Hope this helps others with these problems.