Troubleshooting 12V Trailer Power Circuit on 7-Way on 2008 Toyota Tacoma with Factory 7-Way

Updated 01/10/2017 | Published 01/09/2017

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Pollak Circuit Breaker - Cycling/Automatic Reset - 40 Amp - Straight Mount Bracket

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10 Gauge Wire - Blue Primary - Per Foot

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Hook Probe Circuit Tester

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Question:

My 2008 Tacoma V6 PreRunner came with a factory 7-pin connector, but, for some reason, it doesnt charge the battery in our travel trailer while driving. I suspect that the wire for this purpose wasnt installed at the factory, so Id like to know the best way to install a cable of sufficient amperage to be able to charge the trailer battery while driving the truck.

asked by: Larry P

Expert Reply:

The first thing I would check is that there is a fuse of the correct value in the Tacoma's power distribution box for any circuits labelled trailer/towing/12V power. It is more likely that a fuse could be missing than that Toyota installed a 7-way but left out the one circuit. However, if this is indeed the case, and there is simply no wire connected to the 7-way for the 12V power pin at the 1-o-clock position (see linked photo, please) then you can use 10-gauge wire # 10-1-1 and a 40-amp breaker # PK54540 connected between the battery + post and the 7-way.

If you have a circuit tester like # PTW2993 you can ground the tester and test the 1-o-clock pin on the 7-way socket when the truck is running to see if there is a 12V signal there. If there is a signal, then the issue is probably on the trailer side. Do note that the 12V power feed on a 7-way CANNOT re-charge a depleted battery; it delivers enough current only to maintain a charged battery while you drive. If your battery is depleted, it will not take a full charge via the 7-way no matter how far you drive.

If you have power at the socket, then check the 7-way plug on the trailer for any signs of damage or corrosion on the pin that mates with the 1-o-clock contact in the socket. Check for a bent pin, trapped dirt or even slight greenish or whitish discoloration on the metal contact surface since even slight corrosion like this can cause problems with signal transmission. I also suggest verifying that the battery is charged and in good shape.

expert reply by: Adam R