[JRTJH]

The yellow wire in the TRUCK umbilical is the "accessory feed" and is typically used for the backup lights. Keystone does not install backup lights on the majority of their trailers, so the yellow wire in the umbilical is "not used by Keystone".

The blue wire in the TRUCK umbilical is the "brake feed" for the trailer electric brakes. It connects to one of the black wires. The other two black wires "should be the emergency breakaway switch wires"... One will be connected to the battery feed and the other will be connected to the ground terminal.

VERIFY THAT YOUR TRAILER IS WIRED THIS WAY BEFORE ASSUMING THAT KEYSTONE BUILT AND WIRED YOUR TRAILER THE SAME WAY AS THE ONE THAT PRECEEDED IT DOWN THE ASSEMBLY LINE........