Trailer Lights Do Not Work After Turning on Running Lights On A 1998 Toyota Tacoma  

Question:

Expert Reply:

Typically when something like this happens, it will mean you have a bad ground somewhere. This can be on either your truck or your trailer, though in your case, it is most likely the trailer.

You will need to check all your ground sources to make sure they are not corroded or disconnected, but also to make sure they are not stacked with other sources. This is a fairly common practice, but it can cause issues and it is best for each ground to have its own designated source. Especially brakes and LED lights. However, if all these look good or if repairing them doesn't fix the issue, the issue will be on the truck.

This could be caused by a few things, but ground is still the most likely culprit. Especially on an aftermarket added on wiring system. Again, make sure the ground is good and solid and not stacked. If this doesn't get them working, you will most likely need to replace the wiring on your truck as something has shorted and is causing the issue. This can be verified by using something like the # PTW2993 circuit tester on the running light wire. This will be the 11 o'clock position for a 7 Way and the brown wire on a 4 Flat.

If this is an aftermarket system and you have a 7 Way piggybacking off the 4 Flat, the best option will be to replace the 4 Flat with the Tekonsha T-One Harness # 118379, and then the 7 Way with the Hopkins Adapter 4-Pole to 7-Pole and 4-Pole # 37185. These should get you back up and running if it turns out to be the vehicle side that is causing the issue.

expert reply by: Lazer S

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