Hello all.
I have a 2017 F-250 SD with a running light issue. When hooked to my utility trailer, I have no running lights. When checking both plugs, I only get 3.5 volts from the running light pins. I have seen this issue in other forum threads but have not seen any solutions. Thanks for any help I can get.

 

 

Thanks for your reply. The ground is good, I ran all new wiring including the ground wire. Still same problem, 3.5 volts on running lights pins when not plugged in. All other lights working properly. I have removed trailer settings and reinstalled new trailer in the options. Got to be something I'm missing. I did rewire it with the 4 pin flat plug.

 

Do the signal lines work ok?

 

Yes, signal lights and brake lights work properly. I'm thinking something needs reset in the trailer logic. I can't figure out why it shows 3.5 volts, you would think it would have 12 volts or nothing if there was a bad fuse or something like that. I might have to take it to where my camper is and hook it up to the camper and see if the 12 volt running lights work when hooked to it. Any help or suggestions would be greatly appreciated. I read one reply somewhere that said they had to turn off daytime running light to get the trailer lights to work properly, but that doesn't make sense to me but might give it a try. Thanks

 

I think it is okay since the lights works. The voltage is there all the time so when it detects a current it knows a trailer is connected without turning lights on.

 

 

Thanks everyone for the replies. I think I understand now why the 3.5 volts, to sense when trailer is hooked up. But how does the truck logic pick up the trailer hooked up on the 4 pin plug? The last time that it was hooked to my camper, just a couple weeks ago, with 7 pin plug it worked fine. So just wondering if the 4 pin plug is the problem. Just thinking out loud. I might have to find another trailer with a 4 pin plug to try it on.

 

 

This is a problem I had with my '17 SD after a couple visits to dealer they found a bent/damaged pin in one of the connectors on truck. I f I recall they indicate it was a connector near the front. I know others have had moisture in connectors in rear of truck Search the forum here this isn't the first time this issue has been reported

 

Never mind posted to wrong thread

 

I have a 2017 F350 CCLB. If I am not mistaken, when I hook up my RV the running lights don't come on until I turn on my truck lights. Only the break lights work. Which doesn't make sense because on my old Chevrolet, as soon as I plugged in the RV all of the lights came on.

 

truckzilla - you're ford is working the way most trucks have always worked. Sounds like there was something up with your Chevy.

 

Thanks to all. I did have the truck parking lights turned on and wasn't t getting the running light on the trailer. I will probably pick up one of those test plugs and see what it says. I am going to tale truck to where my camper is and hook up the 7 pin plug to make sure the running lights are still working thru it. Hoping to avoid trip to the dealer but might have to. Thanks again.

 

Had a pretty similar issue. Brand new wiring harness. Brand new truck. Now you would not think that the brand new truck would have a blown 30 amp fuse. Just as
you would not think the plug head on the wiring harness would have 2 wires touching inside it. My son in law(multimeter pro) tested it and found way to much resistance
in the plug where there should not be any. Cut the old plug off, wire it on' no resistance but still would not work. Checked all the other wires for continuity from tail lights
to the plug. All good. He went under the hood and was headed for the very same 30 amp fuse that the dealer replaced. I just got tired of scratching my head. Any way
there was a lot more testing and head scratching I leaving out. Now the 3.5 volts is a puzzler. I did not have any power for the brown wire(running lights) Also the lights
ground thru the bolts. So using the ground wire or even having it on the trailer hitch makes no difference when everything is right.. I can get you the service write up for
the specific fuse. Its top right hand corner facing the truck . Maybe this will help somehow.