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Troubleshooting No Brake Lights on 2004 Acura TL with Trailer Connector Installed


Recently purchased a trailer wiring harness number 118489 for my 2004 Acura TL. Installed the harness per instructions, but I have no trailer brake lights when I hook the trailer to the harness. Also, the cars brake lights dont work when the trailer is hook into the harness as well. All other functions work well i.e., running lights and turn signals. I checked voltage on the 4-pin connector, there is only about 6vdc out of the green or yellow output when the brakes are applied. Any suggestions you could provide would be helpful. Thanks.


Expert Reply:

Lets see if we can get you going. Let me know if any of the suggestions that I make sound like they will work or if you have already checked the suggestions I make here.

When you checked the output at the 4-Way connector was the trailer hooked up? If so unhook the trailer and recheck the voltage. If you have twelve volts at the green and yellow connections on the 4-Way harness without the trailer connected then the problem is most likely a ground issue on the trailer side. Check all of the grounds on the trailer. If the lights are grounded through their connections to the trailer frame make sure something is not causing a bad ground like a plastic license plate bracket or rust paint or corrosion at the ground studs. If the lights have separate ground wires check each one of these. If the light brackets are bolted to the trailer make sure that rust, paint or corrosion are not keeping the bracket from making a good ground contact to the trailer frame. Also check the ground wire at the coupler and make sure it is securely grounded.

If the connector is only showing 6 volts at the rear of the vehicle when the brakes are applied, and the trailer is not connected, then you will need to make sure that the ground wire on the harness, # 118489, is connected to clean, paint and rust free chassis ground.

If this does not solve the problem check the wiring going into the converter. You should have turn signals on the yellow and green wire brake light on the red wire and tail lights on the brown wire. If the signals going into the converter are good and the signals coming out do not have the proper voltage, the converter has most likely been shorted in some way and will need to be replaced.

If this is the case you may want to go with a splice in powered converter with circuit protection, item # C56496. This type of harness powers the trailer lighting with the vehicle battery and only uses the vehicles wiring as the switch to send power for the correct function on the trailer. A separate power wire with inline fuse is needed for this installation, item # 118151.

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