Troubleshooting New Electric Drum Brakes on Utility Trailer That Do Not Engage with GMC Controller
Question:
Electric brakes not responding on utility trailer. Installed e trailer 7 way plug, junction box and new brake assemblies. 2010 GMC with factory tow/controller. Shows connections and brakes when hooked to my RV but not utility trailer.
asked by: Ed
Helpful Expert Reply:
Since your 2010 GMC Sierra's factory-installed brake controller is properly engaging the brakes on your RV trailer we can start out troubleshooting by checking on the utility trailer's wiring since this is newly installed.
The easiest way to test the brakes on the trailer is to do so independently of the truck. You can do this by disconnecting the truck/trailer connectors and applying 12V power and ground directly to the contacts on the trailer's plug. Please refer to the linked photo that shows a trailer-side 7-way plug and the RV-standard wiring configuration for each circuit. In this case the ground pin is at the 5-o-clock position and the brake circuit contact is at the 7-o-clock position as you look at the plug.
You can use a spare 12V battery (or the one in the truck) to provide the power for testing. You should be able to hear the brakes humming slightly when they get this full 12V power input and certainly if you try to rotate a wheel you should feel that the brake is engaged. Note also that you can test all the lighting functions on the trailer in this very same way.
If the brakes do not engage with direct power input odds are that there is a mis-wired circuit in the junction box you installed. There are several different wiring schemes for trailers, and these are shown in the linked article on trailer wiring. It is possible that your two trailers are wired differently from one another, and this certainly could cause the issue you're having with the utility trailer. On the plus side, since you have wisely used a junction box to make your wiring connections if the problem is a mis-wired circuit it will be easy to correct this by changing the location of the brake circuit ring terminal to the correct post in the box.
Different brands of 7-way trailer plugs can use varying wire colors for each particular circuit. Often a blue wire is used for a trailer brake circuit, such as with Hopkins # H20046 that you referenced. However, similar part # 54006-009 from Bargman uses a black wire for the brake circuit. Be sure to match the wiring from the trailer plug to the wiring out to the trailer brakes by function, not color. A circuit tester like # PTW2993 makes this easier.
There may also be a grounding problem. Check the main ground wire on the trailer connector where it joins the frame. The ground needs to be firmly attached to a clean bare metal surface. Check also the ground wires at each individual brake assembly as these, too, have to be securely fastened to a clean bare metal spot on the frame.
If your utility trailer happens to have an aluminum frame or a folding tongue these features can cause problems when trying to make a good ground connection. In these cases, you may need to run a ground jumper wire right from the brakes up to the junction box to ensure a good ground.
Products Referenced in This Question
7-Way Molded Trailer End with 6' Cable - HD Blue Insulated
- Trailer Wiring
- Trailer Connectors
- Trailer End Connector
- 6 - 10 Feet Long
- Plug and Lead
- 7 Round - Blade
- Bargman
more information >
Product Page this Question was Asked From
Hopkins 7-Way RV Style Connector with Molded Cable - Trailer End - 8' Long - RV Standard
- Trailer Wiring
- Trailer Connectors
- Trailer End Connector
- 6 - 10 Feet Long
- Plug and Lead
- 7 Round - Blade
- Hopkins
more information >
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