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Dan, ASE Certified Technician
Category: Ford
Satisfied Customers: 1668
Experience:  Auto Technician
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Hope you have a suggestion for me. My 2003 F350 4 door 4wd

Customer Question

Hope you have a suggestion for me. My 2003 F350 4 door 4wd with 5.4 L motor has a problem with the trailer plugs. Both the 4 pin inline and the 7 pin round will not bring on th e tail lights or running lights of any trailer or camper that i hook up to. i know the trailer wiring is good. Turn signals, brake and flashers work normally but no tail lights. Don't have an owners manual but i pulled all the small fuses in the panel below and left of steering wheel but none were blown. I think that's the only fuse panel. Tail lights on the truck work fine. My Haynes manual is no help. I have a good digital meter but don't know how to diagnose the problem. any direction would be greatly appreciated.
JA: Have you checked the bulbs? Have you checked the connection?
Customer: Replaced bulbs on the small utility trailer but that didn't help. Hooked to a 28ft camper last night that had just been unhooked from my brothers truck and it was working for him. Pulled a 16 ft trailer about a month ago and all was well then.
JA: Are you fixing your F350 yourself? What have you tried so far?
Customer: Yes. Looked at the wiring underneath the back bumper. The wiring comes down in a flex conduit and then branches to the 4pin flat and 7pin round factory sockets Didn't see anything loose, broken or rubbed. Other than checking the fuses which were good, that's about all ive done.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Wish i knew more to ask but, nope , that's about it. And thanks for your help.
Submitted: 9 months ago.
Category: Ford
Expert:  Dan replied 9 months ago.

Hello my name is***** am an ASE Master Technician and I am glad to help you out with your question.

Expert:  Dan replied 9 months ago.

There is a hidden fuse inline of the power wire to the trailer connectors. It is usually under the hood near the fuse box, not it the fuse box but on the wire. Look for a black rubber plug with a fuse in it. It could be in the rear, near the hitch or behind a tail lamp assembly.

I have seen this problem before with the running lights and its always a blown hidden fuse.

Expert:  Dan replied 9 months ago.

Please reply to this if you need more help and we can continue this conversation. This does not have to be my only answer. If you are satisfied with my service, please rate at the top of the screen. Rating does not close out your question. Remember, sometimes it is difficult to completely diagnose your vehicle without being there, but I will try to give you the best answer I can. Hoping to be giving you 5 star service.



Customer: replied 9 months ago.
Thanks Dan. I'll give it a look in the morning. Appreciate the help.
Expert:  Dan replied 9 months ago.

Your welcome.

Expert:  Dan replied 9 months ago.

Hello again Dan here,

I am contacting you because the post has not been closed or rated.

This question is coming up on 7 days which means it will time out and close.

You have already paid to get this question answered, but you have not rated.

Let me help some more. Is there anything else I can help you with?

If I did not give you 5 star service, please let me know what I missed.