Troubleshooting RV Electric Brakes That Do Not Engage  

Question:

Expert Reply:

Since you have tried your truck with another RV trailer and found that trailer's brakes worked fine with your truck and its brake controller this suggests the problem is on the trailer side.

There is a simple test you can do on your trailer's brakes that needs only a well-charged battery, such as the one in your truck. If you connect wires to the battery and directly apply their other ends to the brake and ground contacts on the trailer's 7-way (see photo please) all brakes on the trailer should lock up since they'll be getting a full 12V signal.

If they do not you can use a tester like # PTW2993 to probe the wiring between the 7-way plug and each brake assembly to find the point where power is lost so that you can repair or replace that damaged wiring. You can also perform this same test right at each one of the individual brake assemblies. This makes quick work of finding out where the problem is.

If you have a multimeter like # PT89ZR you can test the wiring in the same way but this will allow you to check for the actual voltage reaching the brakes. For example, if you test at one point on the trailer and read about 12V but at another point further downstream you read less voltage then you know to check the wiring in between those points to look for a short from a pinched wire or cracked insulation.

If your brake grounds are made at the trailer frame you might try sanding off those ground points to expose clean bare metal. Paint, primer, grease or rust can interfere with the ground connection that is critical for the brakes (and lights) to function. If a brake will lock up fully with the direct battery connection to its two wire leads then this does suggest the grounding at the trailer is the issue. You can also try running a ground jumper wire from each brake to a junction box like # HS381-9000 which will remove the trailer frame from the brake circuit.

expert reply by: Adam R

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