Just went to pick up my trailer from the storage facility. Only 500 miles on the truck and this is the first time I've hooked up. The trailer has been in storage since August when we got back from a 2400 mile road trip. The tow vehicle for that trip was my 2005 V10 F250. The truck and trailer performed flawlessly. Upon connecting the trailer this morning, the truck immediately recognized it's presence. It went through the checklist: Trailer connected, do you want to add a trailer, trailer light check, BLIS turned off, etc. Turned on the right blinker and the truck registered a left blinker fault. I sprayed contact cleaner on the truck and trailer sides of the 7 pin connector and made sure it was well seated. Home isn't too far away, so I decided I would deal with it there. Put my foot on the brake to shift into drive and the trailer disconnected message came on but I could see that the trailer marker lights were still on. I manually activated the trailer brakes and they engaged. The trailer and truck were obviously connected in spite of what the truck was telling me. On the drive home, I got multiple messages; trailer connected, trailer disconnected, blinker and brake light faults. The brake lights and and blinkers do function, but faintly. Checked the connections behind the bumper and they felt solid. What's going on here?

 

I am sure this will be the first place you will look but grounds are the #1 electrical problem with trailer. I would be looking where the trailer ground wire connects to the trailer frame.

 

I would take the truck back in and have them check the 7 pin connectors, truck side.

 

Are the house batteries fully charged and battery disconnect switch closed? Without house batteries the e-brake will send a disconnect signal. Ask me how I know.

 

The older trailer plug (male) wasn't fully seating into the younger female receptical...works fine now.

Oh, the double entendres with this post...😁

 

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I had this same issue with an older trailer plug as well. It seems the older style 7-pin male ends don't want to fully seat into the female 7-pin on the newer trucks. It would work fine for a bit then I would get the trailer light fault or trailer disconnected messages after hitting a bump in the road. Its not just a Ford issue either, my buddy's new GMC had the same problem with his 2005 Exiss enclosed trailer. We ended up having to replace the trailer plugs. This is what we ordered: Hopkins 7-Way RV Style Connector with Molded Cable

 

I noticed there was a fairly wide gap between many of the contacts on the female (trailer) side of the 7 pin. Squeezed them together so they actually touched. Shot both sides with contact cleaner again and reconnected. I didn't go for a drive but sitting in front of my house the truck to trailer connection is solid with no fault messages. Hopefully, it is that simple.