I have a 04 FX4 crew cab and when I plug into a trailer harness I have turn signals and brake lights but no night running lights. All fuses are good, any help would be great.

 

Has it ever worked before ?

Did you check the trailer tow parking lamp fuse, and make sure that the traielr tow parking lamp relay was installed ?

Have you checked both the flat 4, and the 7 pin parking lamp terminal for power when the truck's parking lamps on are on ?

 

I dont know if it ever worked I bought the truck used. I did check all the fuses. I dont have running lights on both the 4 flat and 7 pin.

 

I've had this problem before. It ended up being a ground problem to the running lights. Like it wasnt "connecting right" (ford mechanic)

 

the connector at the back of the 7 pin and 4 flat plug looks ok also and wires all are still wrapped from factory

 

Why did you check the fuse for the radio and the headlights ?

 

I didnt check the fuse for the radio just all the lights

 

Ok, now we are getting some info, you said all fuses before.

You checked all the lights, but did you check the trailer fuses ? They are different then the truck parking lamps.

Also you did not say if you checked if the trailer tow parking lamp relay was installed.

 

yes i did check the trailer fuses. the trailer tow parking lamp relay is installed

 

i guess i should make sure im not missing a fuse box. i checked the fuse box in the passenger front kick panel and the little relay box drivers side under the hood.

 

Nope, those are the only ones.

Trailer tow fuses are in the cab of the truck.

When you test for power at the trailer tow adapters, which pins are you using, and what are you using for ground ?

Quick test, pull the trailer tow parking lamp relay, and jumper the normally open to the common terminals. That would put power at the trailer tow adapter regardless of the position of the main headlamp switch.

 

i cant remember what pin it is im testing the cover of the 7 pin tells what each pin is for so im just going by that. as for the ground im going straight off of the battery, i have a tester that i can go from the front of the truck all the way to the back. I will have to try to pull the relay and see where i get.

 

i just took the relay out and still no trailer lights

 

How about this route.

Pull the trailer tow parking lamp relay, and test for power on the common pin.

This should be R201 in the fuse panel, a half size ISO relay.

The power from Fuse F10 is on pin #3. Test here to the battery ground for power.
The circuit to the 4 pin / 7 pin trailer tow adapters is from pin 5.

This is what you are looking at for the relay


If pin 3 in the socket is dead, there is a problem with Fuse F10, or the fuse panel itself ( not likely, unless you have had it out for some reason ).

To check the ground on the relay socket, use the ohm setting from pin 1 to the battery ground terminal.

To check that the headlamp switch is turning the relay on, turn the headlamps to the park or head position, and check for power on pin 2,

If you meter leads are long enough to go front to rear, check for continuity on pin 5 of the relay socket to the trailer tow adapters.

The 4 pin is easy, the ground is the exposed pin, the 3 remaining, the center is the parking lamps.

The 7 pin :


If you have the fog lamp relay installed, you can try swapping them, the fog lamp relay should be the same size relay ( 1/2 ISO ).
give that a try.

 

ok i will try this tonight and get back to you tomorrow. I did switch the relay with the fog lamp relay and didnt help so i will try this. Thanks so much for your time.