Troubleshooting Right and Left Turn Lights and Brake Lights Not Working on a 2003 Ford F-250 7-Way

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Question:

Everything has worked for years but now when I checked my lights on the travel trailer and/or my enclosed trailer I have no turn lights or brake lights. I have a 2003 Ford F250 6.0 Diesel. I used a meter at the trailer 7 way connector and I have 12V on the black, ground on the green, running lights, trailer brake power but nothing else for the turn signals left or right and no brake lights. I dont have a Ford 2003 owners manual so Im not sure if it may be a fuse problem....I do see that Fuse 19 and 20 10 amp both say trailer tow connector both fuses are good and fuse 101 30 Amp says Trailer tow relay battery charge and fuse 108 30 Amp says Trailer Tow Connector. These two fuses are a square box and I didnt know how to pull them or test them....Ill have to go to Auto Zone and ask them....Anyway, do you have any suggestions of what to check next.....I do have a trailer brake module under my steering wheel that has worked in the past....Ive purchased trailer supplies from you in the past and thought you might have an idea. Thanks

asked by: Dan S

1

Helpful Expert Reply:

You have done a great job troubleshooting the problem so far and have isolated the issue to the truck wiring.

I have confirmed with my contact at Tekonsha, and another fuse that you might check would be fuse # 6 in the under dash junction box. This is a fuse for the trailer towing light relay. This will be a 20 amp fuse. This sounds like this is the fuse that is most likely causing the issues on your 2003 Ford F-250, since you do not have either brake or turn signals. The # 6 fuse is for the relay that would combine the turn signals and brake signals for a 4-way trailer connection.

Another fuse to check would be the stop light fuse, or possibly the center high mount stop light (CHMSL) fuse. If this fuse is out it might also be causing some issues at your truck 7-way connection point. If this fuse is bad it might be why you do not have the turn signals or brake lights. However, if the signals on your truck are functioning properly this may not be the problem fuse.

Since you did test the 7-way, and you do have 12V at the black wire at the vehicle connection point. Then it sounds like the 30 amp fuse that you indicate as 101 trailer tow relay battery charge is good.

It is possible that the other 30 amp fuse that you mention, in the 108 position, indicating the trailer tow connector, might be bad. However, since there is signal for some of the functions at the 7-way I do not believe this would be the issue.

If you have checked all the fuses and they are all good, you might have to trace the wires under your truck to see if there is any indication of damage to the wiring. Pay close attention to wiring near hot areas and moving areas like the exhaust and suspension.

It would also be good to take a look the the blades on your 7-way connection and make sure that there are no loose connection points, any signs of corrosion, or any other damage to the connection points. This might also be causing the problem.

Please note that if you do find a bad fuse on your truck and you reconnect to your trailer that has a short a fuse may fail again. I recommend taking a look at your trailer wiring, and making sure that everything is properly ground and to do a quick inspection of the wires, making sure they are in good condition.

I have included a helpful article on trailer wiring for your reference.

expert reply by: Rachael H

1

Troubleshooting Right and Left Turn Lights and Brake Lights Not Working on a 2003 Ford F-250 7-Way

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