Mille Racer 69

Hey all!
I have an issue with with my '95 silverado.
So you know how there are generally 3 brake lights on trucks:
-the light above your rear window between your cargo/load lights
-your 2 standard lights, 1 on both sides of the tailgate.


I just bought this truick and noticed the bulbs for the cargo lights and the brake light above the rear window were burnt out so I bought 4 new bulbs. The 2 brake lights on either side of the tailgate both work fine.

Well the cargo light I replaced but still won't work, but my beef is with the brake lights right now. I put 2 new bulbs in, stepped on the brakes and all of the suddon I have no brakelights AT ALL - none. the 2 that were previously working on both sides of my tailgate are non-op.
I take the 2 bulbs back out and now my 2 brakelights on both sides of the trailgate are working again. I repeated just to make sure and of coarse it did it again.

any ideas on WTF is going on?

Thanks!
~Nathan