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Brake Controller Recommendation for a Truck with Air Brakes and a Trailer with Electric Brakes  

Question:

I just purchased a 33 gvw truck with air brakes. I thought I could simply plug in to the 7 point connector to the back of truck and connect to the trailer. The trailer has all the dot safety and break away controls on it. I was told that the truck needs a converter from air to electric. Seems strange since I have electric for lights.

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Expert Reply:

The trailer brakes work on a separate circuit than the lights. You have a couple of options to control the electric brakes on the trailer.

One option is to use an air over electric brake control, # HA100400C. This unit connects to the air brakes on the truck and when the brakes are applied it sends an electric signal back to the trailer brakes.

The other option, and what I would do, is to use an electric brake controller like # 90885. For either of these controllers, the red wire attaches to the cold side of the brake switch or any dedicated brake light circuit, like the center high mount stop light (CHMSL). It must connect to a wire that only shows power when the brake is pressed and not also when the turn signals or running lights are on.

The black wire connects to the positive battery terminal on the vehicle via a 20 amp circuit breaker # PK54520 for 2 to 4 brakes or a 30 amp circuit breaker # PK54530 for 6 to 8 brakes.

The blue wire will connect to the back of the 7-Way in the 7:00 position. On # 90885, the white wire grounds to the negative battery terminal. I have included a link to the isntallation details for 90885.

expert reply by:
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Michael H

John S.

7/13/2024

90885 brake controller will not operate trailer brakes properly. Those brake controllers look for truck nose to dip to operate the proportional brake control which larger (with air brakes) truck do not do. Only an air over electric brake controller will operate brake properly, like the HA100400C

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