2001 Chevy Venture Brake lights

Thank you for your quick response. I don't have any towing wiring and I just got done replacing the multifunction switch. Still no go. The brake lights do now work but if I have the lights on, press on the break, and have the left side blinker going it doesn't work properly/ The brake light and the blinker dim out and alternately flash. I am assuming I have a short somewhere.

I have the exact same issue with my 2003. Been trying to figure it out for a while.

Thank you very much for the wiring diagrams. They will be very helpful. I did find a corroded probe on the top of the drivers side lighting assembly. I swapped the two tail light assemblies around to see if the problem would move to the passenger side and when I did it the lights worked fine. I moved the drivers side assembly back to it's normal side and the problem came back. I ran to the local salvage yard and got a new one and put it in and so far so good. Hopefully that is all it was. FYI for anybody interested. The multifunction assembly and switch (the turn signal switch) cost almost 300 dollars from a dealer (apparently an auto parts store cannot order one) so if you can find one they are rather common at salvage yards because the same assembly is used on all Ventures from 95' to 05'. With removal it only cost me $60. I also got a whole tail light assembly for $30 instead of the $80 that the dealership wanted to charge me. Once again, thank you for all of your help.

I sent my venture to my mechanic for an oil change and told him to try and fix the lights. They seem okay, but he wasnt there so I dont know what he did. I had previously changed the whole assemblies from salvage also. It had not worked