I have a 2004 ford f350 and I cant get the trailer lights to work. I have checked for voltage for blinkers, brake lights, running lights, reverse lights, 12v wire, and trailer brakes and they all have power. I also checked my grounds and they are good and I even cleaned them up. I have hooked up to 4 different trailers and the lights still do not turn on so I believe it has something to do with the truck. I did manage to get the running lights to come on but still nothing else is working. Its a brand new 7 pin connector and also one of the trailers I hooked up to have lights on the trailer connector to tell what has power and what doesn't and says my AUX 12v is the only power its receiving. Anyone know what could be the issue?

 

At this point we don't know where the cord from the truck to the trailer came from or if it ever worked before.

Starting at the back of the F350,
What do you have power and where , I would strongly suggest using a simple test light. At the rear of the F350, you should have parking light power to one of the 7 way pins , If that is what you have there.
With key on, 4 ways activated , you should have 2 pins that will cause the test light to flash. Do you have those 3 things at this time ?
Our reasoning here is to verify the signal is present to send to the trailer.
Depending on if we have those signals coming out of the F350 will determine where we go next.
Which pins have that power?

 

Thanks for the help. I have power at the connector at all the pins when I should have power. Here is what I got for the voltage readings. Brake/Blinkers ≈ 10.5 volts, AUX ≈ 14v, Backup lights ≈ 12v, Running lights ≈ 12v. Ground has continuity from grounding location to the pin and I cleaned the ground so its now bare metal to bare metal. I have power and ground just cant figure out why the trailer lights wont come on. Like I said earlier though I have running lights on the trailer and thats it. I know its not the trailer because other trucks can hook up to it just fine. Im completely lost. I checked all fuses and relays too just incase and everything is good.

 

Did you , verify the pin where you had power at the truck ,ALSO had power at the same pin at the other end of the cord?

If ,,,,,,,,,,you have a cord that has a molded plug , that should be wired correctly
If the plug is made so it can be opened and the proper colored wire as power at both ends . Sometimes for example the brown wire , which usually is for parking lamps ,
Can be connected to the right pin at one end and wrong pin at the other end. All these things need to be checked and verified. The main thing here is to verify the truck is sending power out of the right pins when the selection is made. If we don't have the right pins providing power from the truck , nothing can work correctly until this is straightened out first.

 

Just type in on your computer search, ford 7 way plug wiring diagram, and you can see and decide which applies to your set up.

 

The plug is molded and works on other trucks. I looked up one of those diagrams up when I was wiring the new 7 pin connector and double checked with a multimeter making sure reverse light pin had voltage when in reverse, brake light pin had voltage when brakes applied etc. Everything is wired correctly and everything has power. Was thinking maybe a ground but I cleaned the ground and I even added an extra ground just incase.

 

If you verified all is what it is supposed to be at your truck, IT would not be the first time somebody else messed with those trailers.

Just a reminder, if you know you have power coming out of your truck and the cord is molded,you also then know you have power at the right pin for the plug that goes to the trailer, . With that much known to be correct , there has to be a problem with the trailer(s) When you are not sure you can get easily confused, but when you have PROVEN everything is right at the truck and the cord ,you can feel confident it is not the truck. You can handle this !

 

Thanks. The trailer im trying to get to light up just got all of its wiring and lights redone about 2 weeks ago and any other truck has no problem lighting up the trailer. I went back with a multimeter again to the 7 pin and everything checks out. I plugged it into the trailer and im getting AUX and runnings lights but nothing else

 

Did you verify left and right turn signal power is available at the back of the 350?

You do need the key to be on for the signal lights to work,correct ?
Do you have signal light power at the back of your truck at the plug, Yes-No ?

Before we can go anywhere , we need ti verify we have signal light power at the plug on the 350. We will either have it or we won't. If we don't, there are 2 relays that send signal light power to the plug at the back of the 350.It would be rare that both relays are defective (left and right). No sense getting involved with those relays until we know where we are.
So many people have been involved in this saga I would not take anybody's word on their work unless I verified it myself. Just because it works on one trailer doesn't mean they were all wired the same.
The main thing we want to verify is, POWER IS AVAILABLE AT THE PLUG ON THE TRUCK WHEN IT IS SUPPOSED TO BE.. Until we do that , we are chasing our tail.
Can you tell us which pins on that plug , not the cord, have power and when, thanks.