Maybe this will help
WORKHORSE Class A Chassis Instructions
Workhorse A-Body Brake Control ConnectorFactory Harness
UTB Wire Color
Electric Brake Output Circuit
Brake Switch Signal
The wires listed above are located under the dash left of the steering column next to the chassis fuses & breakers.
A large black label will be attached to the end of the wire drop identifying it as the Trailer Brake Controller Provision.
Use the table above to attach the Electronic Brake Controller to this wire drop.
Cut the 6-pin connector off the EC-4129 pigtail. Connect the three wires that were attached to the connector to the factory wire drop as outlined in the table above. NOTE:
Circuit identification is printed every four inches on the factory wires.
Find a switched 12-volt source for the remaining (red) wire that was not inserted into the pigtail connector. Splice the red wire from the pigtail into the switched 12-volt source.
Plug the other end of the pigtail into the connector from the Unified Tow Brake controller.