Tekonsha Primus Brake Controller Showing SH Error Code When Trailer is not Connected

Expert Reply:

The SH error code indicates a short circuit in the brake controller output. Since it is occurring when the trailer is not connected, it would eliminate the trailer wiring as being the problem.

The trailer connector itself is the usual suspect in this case. Check the connector for damage or corrosion. If you can see any white or green corrosion on the pins of the connector, there is a good chance that the corrosion has spread to the interior of the connector, where the wiring connects to the terminals. If this corrosion becomes severe enough and builds up on the terminals, it can cause a short to an adjacent terminal.

If the connector checks out okay, locate the blue wire exiting the rear of the controller. Sever the wire several inches rearward of the controller (so there is plenty of available wire to reconnect it). If cutting the wire solves the problem, the short exists somewhere in the wiring between the connector and the brake controller. You can trace the wire if you care to, looking for loose connections or worn or cracked insulation, but this might be difficult depending on the vehicle. Your best bet might be to simply tap in a length of 10 gauge wire like # 10-1-1 and run it from the blue wire on the controller to the # 2 terminal on the connector. This would bypass the defective wire.

expert reply by: Mike L