Interior Trailer Lights Do Not Work When Trailer is Connected to a 2012 Toyota Tacoma

Question:

Have a Haulmark Low Hauler. When I hook up the 7 pin connector everything works besides the interior lights in the trailer. Where do I start to troubleshoot? I have searched the internet and have found look under the hood for a wire that needs to be connected for a 12 volt source among other things. I have a 2012 Tacoma. Thanks for the help.

asked by: Jeff P

Expert Reply:

First you will want to test the 12 volt circuit on the truck side 7-Way trailer connector to make sure that it is receiving power. You may need to have the key in the on position in your 2012 Toyota Tacoma to make the 12 volt circuit active.

Using a circuit tester such as # PTW2993, test the pin in the 1 o'clock position. If it does not have power then it could be a blown or missing fuse or relay. Use the truck owners manual to find the locations of all the fuses/relays related to the tow package wiring to check them.

If you do have power at the 12 volt circuit on the vehicle side then the issue is likely on the trailer side. Plug in the trailer connector to the truck. Locate the 12 volt circuit at the back of the trailer side 7-Way to test it with the circuit tester. If it is not getting power ten there is a break or loose wire in the connector.

Keep tracing the power wire back. If it terminates before reaching any lights then that would be the problem. It is also possible that the 12 volt power wire from the trailer connector is supposed to go to a trailer mounted battery and then from the battery to the accessory lights. Following the wires will reveal how the trailer is wired and will also allow you to check for any breaks in the wiring.

expert reply by: Michael H