weird brake light issue

[iamseth]

My '72 C10 cheyenne was having some rear turn signal/brake light issues. The passenger side would not work one day, driver side the next, then BOTH sides went out. Magically the next morning they would all function fine and then by the time I made it to work.... one side was out again.

Turns out there was a cob web of wiring that was supposed to be a trailer hook up. Real nasty job. So, I pulled all that out and cleaned it up a bit. All the lights are working, but now this is happening:

When either turn signal is on, NO brake lights work.

Has anyone ever seen this before? After looking at the wiring diagram, it seems to me the brake/turn signal is fed by the same wire. I don't understand why the driver side rear brake light won't work when the passenger side turn signal is on and vise versa.

Thoughts?? Sorry for the long explanation.