Testing to Determine Why The Tail Light Circuit is Inoperative on a 2003 ford F-150 Pickup

Question:

i have replace my 4 flat plug with a7 pin wireing harness but my tale light on my trailor will not work. the brake, turn signial and brakelight work. what is wrong????????

asked by: bennie m

Expert Reply:

I would start troubleshooting by using a circuit tester, item # 3808 if needed, to determine if the tail light circuit is active on the vehicle side trailer connector. If so there is a problem on the trailer.

If not check the vehicle side plug that the Tow Ready Custom Fit Vehicle Wiring for the 2003 Ford F-150, item # 118242, plugs into. If this circuit is functioning properly then check the wires coming out of the new connector to determine if the power is getting to the 7-Way harness. If not there is most likely a problem with the connection.

If power is not found at the vehicle side connector, check the fuses in the power distribution panel which is located either under the hood or under the dash behind the panel below the steering column. There should be a tow package fuse for the tail light circuit and this may be the problem.

Since you had a 4-Way previously you should have the proper circuit ran to the connector on the frame rail at the rear of the vehicle, unless the 4-Way was hard wired. If the 4-Way was hard wired the possibility is that the tail light circuit was not wired to the connector from the factory. In this case you will need to use the tail light circuit wire from the hard wired 4-way and tap into the # 118242 wiring harnesses tail light circuit to make this circuit function.

expert reply by: Robert G