my brake lights only work when ignition is off?

[94.Sierra]

I swapped engine and transmissions out. The transmission/t-case connectors aren't plugged in (used different transmission and a lock-up harness to control shifts). The 3rd brake light/brake light on top of cab its bulb is burnt out. The other brake lights work only when the ignition is off, when I put the key in the ignition and turn it to the accessory position they don't work, same with when the truck is running. Pull the key out, brake lights work. Any ideas what could be going wrong? Trucks a 1994 RCLB, 4.3/700r4. Originally came with a 4.3/4L60E.

 

[Wagonbacker9]

Likely the transmission connector has a connection that the brake lights need. If I had to bet, its for the shift lockout as well, so right now you can probably shift it without stepping on the brake.