trailer 4pin flatwire connector
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Junior Member
Joined: Dec 2004
Posts: 6
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From: New Jersey
trailer 4pin flatwire connector
Just hooked my boat to new F150. when I plugged my trailer in my lights acted strange. No turn signal lights, and running lights were dim. Hooked trailer to wife's Ranger and lights OK. Put a flat connector tester into plug on truck and it only shows running light working and not turn signals. I wanted to fish ASAP. anybody got anything I should look for or a quick solution, I can make an appt with dealer,but who want's to wait, I want to fish tomorrow. Is there any difference in the wiring on this system that would make a standard 4 flat not work. By the way the truck is an 04 and came with the plug pre wired for trailer, not my handywork this time.
Senior Member
Joined: Mar 2001
Posts: 3,248
Likes: 2
From: Rochester, NY, USA
I'd be willing to guess that you've blown at least one fuse - maybe more - on your trailer circuit(s). Your Owner's Manual (or SSCULLY if he chimes in) will show you where the fuses are so you can replace them. How did they blow? The standard 4 pin trailer plug pretty much hangs out there just looking for junk to fill it up and short it out. Then you find out when it's time to fish. You might want to clean out the connections and coat them with at least WD-40, or better yet, Dielectric Grease to prevent future shorts.
Technical Article Contributor
Joined: Jun 2002
Posts: 10,511
Likes: 10
From: Under the flightpath of old ORD 22R
How did you know I would find this :D
BTurville,
Here is the fuse diagram for the '06, I think it is still 1:1 with the '04 Both F36 and F42 are for the tail lamps.
Do you have the same problem, with dim running lamps and no turn / stop lamps ?
Dim tail lamps might indicate that there is not a ground in the system, and it is finding a ( weak ) ground via another method, like maybe the ball ?
Also there is a Trailer tow parking lamp relay # 201
Flat 4 diagram, in case you don't have it :
Take a meter, and check from ground on the flat 4 to the individual leads, to see if you have power at the flat 4.
Do you have a round 7 pin on the truck as well ?
You can test the lead functions on the 7 pin round to see if it is a connector problem with the flat 4, or if we need to move forward in the harness ( towards the CJB ) to see if there is a problem upstream.
You can follow where the 4 & 7 pin adapters go up by the cross member in this diagram :
The ground from the 7 pin is above that cross member that is between the bumper and the spare tire. It is easier to get to if you drop the spare tire. If you follow item 2, in the diagram above, up towards the frame, you will see the connector ( show in the diagram ,but not marked. )
Here is the fuse diagram for the '06, I think it is still 1:1 with the '04 Both F36 and F42 are for the tail lamps.
Do you have the same problem, with dim running lamps and no turn / stop lamps ?
Dim tail lamps might indicate that there is not a ground in the system, and it is finding a ( weak ) ground via another method, like maybe the ball ?
Also there is a Trailer tow parking lamp relay # 201
Flat 4 diagram, in case you don't have it :
Take a meter, and check from ground on the flat 4 to the individual leads, to see if you have power at the flat 4.
Do you have a round 7 pin on the truck as well ?
You can test the lead functions on the 7 pin round to see if it is a connector problem with the flat 4, or if we need to move forward in the harness ( towards the CJB ) to see if there is a problem upstream.
You can follow where the 4 & 7 pin adapters go up by the cross member in this diagram :
The ground from the 7 pin is above that cross member that is between the bumper and the spare tire. It is easier to get to if you drop the spare tire. If you follow item 2, in the diagram above, up towards the frame, you will see the connector ( show in the diagram ,but not marked. )