Sawyer 56

On my 95 SLT2500 that was the brake wire that went to the back to power the trailer brakes. The 95 was pre plug and play you will most likely end up cutting the plug off your brake controller and hard wireing it , they were thinking about plug and play but didn't quite get it together in 95. The easiest place to get the brake feed for the controller is right at the brake switch since this is only a signal wire to the controller it won't overload the brake light circuit. The actual power for the trailer brake circuit is through the fused input to the controller.

joem

Yup your correct Sawyer, I found out that in 1994-1995 they only had the blue out wire. Then in 1996 or 1997 they put in the 4 wire flat pin lead and re-labeled it "electric brake"
I have yet to find out where the blue wire is hidden on the back of the truck