Testing Operation of Trailer Brakes to Determine Cause of Error Message

Updated 03/11/2019 | Published 03/08/2019

Question:

When troubleshooting the brake controller Im getting some odd results. Im getting an S.H code when I connect up the unit unless I cycle the boost button or activate the manual slide knob in which case the indications seem normal. With a voltage meter on the blue wire and just the black wire connected to the battery Im getting up to 11volts on the blue wire. Once I connect the white wire to ground, the blue wire s to 0.3volts and the display behaves as previously described. The blue wire voltage stays around 0.3 regardless. Is there anything I can do with this unit?

asked by: Mark E

Expert Reply:

Both the Activator brake controller # 5504 and the Primus model # TK90160 will not show actual output voltage when tested with a standard voltmeter. This is noted in the troubleshooting portion of each controller's instructions (both are linked for reference). Some testers will cause this error message.

If your controller activates the brakes correctly when the trailer is hitched then you should be okay. But an actual S.H. code when connected tells you there is a fault on the brake output circuit (typically the blue wire) and I recommend you check this first on the trailer.

You can use a direct battery connection to the brake and ground connections on the trailer plug (see photo please) to see if the brakes engage. This test bypasses the controller and all of the truck wiring so it is a good way to know whether or not any wiring problem is on the trailer side. If you hear the brake magnets hum and the brakes engage then any actual short is more likely to be on the vehicle side.

Trace the brake wire looking for signs of damage, like cracked insulation, bare spots in the insulation, especially where it may contact the vehicle frame or other parts that could over time have caused damage that resulted in the short. The linked articles will help too.

expert reply by: Adam R