X0398379

I've got a 2000 Silverado with a factory 7 pin with no trailer brake kit, I have since installed a p3 90195 kit and E wire plug and play kit under the dash in the junction block, I have 12 bolts hooked up to post 1 with the fuse and now I have the blue wire with the connector on it still, does this need to be extended into the cab to tie into the E wire kit or does that need power as well from post 2 to give the brakes power? I just need to know what I need to do with the blue wire with the connector on it thank you