I have a 2013 F350 Super Duty with factory towing package. Both the right and left tail/turn/stop lights work with no issue. The left side of my 5th wheel does not work when hooked to the trucks trailer connector. The left trailer lights work when powered with an alternate 12v source. The corresponding pins on the truck connector show no power for the left side. I've swapped the relays, 75 and 76 with no change in the problem. Any thoughts on where to go from here?
2013 Trailer Light Connector
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The factory trailer wiring has the trailer circuits separated from the truck lighting circuits by relays and fuses. The trailer relays and fuses are located in the BATTERY JUNCTION BOX located at the left rear of the engine compartment. You can find fuse information and a location diagram in your Owner's guide. If your truck lighting is working properly, and the right trailer turn/stop lamp works, this suggests that the trailer left turn/stop light relay gas failed OR you have an open circuit. Both sides share the same fuse FYI.
Fuse F14 in the Body Control Module (BCM) powers ALL of the truck's left turn/stop lighting as well as powering the trailer relay coil circuit and is module controlled. If that fuse was open, the truck's lighting would also be inoperative... which you report is working properly.
Good Luck!
Tried These
I have done the following:
Fuse 14 in BCM appeared to be normal and I verified this by swapping with 13 the right side fuse with no change in the problem.
In the Battery Junction Box I swapped the right and left side turn stop relays (74/75) with no change in the problem.
I unbolted the trailer connector bracket and discovered some wire chaffing on the yellow left turn/stop yellow wire, the brown tail light wire, and the green right side turn/stop wire. I isolated them from each other and ground, the problem remains unchanged.
I would seem there is a blown fuse or relay somewhere?
I have done the following:
Fuse 14 in BCM appeared to be normal and I verified this by swapping with 13 the right side fuse with no change in the problem.
In the Battery Junction Box I swapped the right and left side turn stop relays (74/75) with no change in the problem.
I unbolted the trailer connector bracket and discovered some wire chaffing on the yellow left turn/stop yellow wire, the brown tail light wire, and the green right side turn/stop wire. I isolated them from each other and ground, the problem remains unchanged.
I would seem there is a blown fuse or relay somewhere?
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No, you have checked and swapped all relevant fuses or relays. Now you need to find the open circuit. Can you hear the trailer left turn signal relay clicking when you move the turn signal switch on for a left turn with the ignition switch in the run position?
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I'm assuming you are using the plug in the bed.
Have you tried plugging the trailer into the connection at your bumper and see what it does?
If that acts normal, the flaw is in the wiring to your beds plug.
I had to drive home that way one time because the bed plug wiring had a short in it.
Just a thought.
Have you tried plugging the trailer into the connection at your bumper and see what it does?
If that acts normal, the flaw is in the wiring to your beds plug.
I had to drive home that way one time because the bed plug wiring had a short in it.
Just a thought.
Not knowing the actual pin numbers I'll have to describe them as viewed from the front of the truck facing the tailgate. With the key in the on position, the front left socket of #74 reads 12V all the others show nothing. With the key in the on position and the left blinker on, the front right socket alternates between 12V and nothing with the blinking of the turn signals. The #75 relay sockets show the same under the same conditions but using the right turn signal.
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Earlier in this thread you stated that you had swapped the relays around and that this left turn relay was not clicking when the turn signals were on. At this point, the ground circuit is suspect. The pin in the socket directly opposite the pin with the alternating 0-12 volts should be a constant ground...
Ford Doctor is quicker, but i'll post anyway. I was outside verifying on my truck.
The socket that has 12 volts on it all the time should be pin #3 on both relays and if you pull fuse F100 (25amp) it would confirm it.
The one that blinks should be pin #1 which is controlled by the BCM to energize the relay coil. You should have pin #2 which is the ground pin and between pin #2 (back left) and pin #1(front right) should be blink 12 volts with the truck lights. With the relay out and the turn signals on, across socket #3 (right back) and Socket #5 (Front left) you should read voltage all the time.
I believe the pin numbers are marked on the bottom of the relay.
The socket that has 12 volts on it all the time should be pin #3 on both relays and if you pull fuse F100 (25amp) it would confirm it.
The one that blinks should be pin #1 which is controlled by the BCM to energize the relay coil. You should have pin #2 which is the ground pin and between pin #2 (back left) and pin #1(front right) should be blink 12 volts with the truck lights. With the relay out and the turn signals on, across socket #3 (right back) and Socket #5 (Front left) you should read voltage all the time.
I believe the pin numbers are marked on the bottom of the relay.
I removed both #74 and #75 relays and found, as before the front left socket had a constant 12V with the key on and the front right powered on and off with the respective turn signal blinking. I also confirmed the rear left socket is constant ground for both relays. Here's the head scratcher. After removing the #74 relay, I noticed a crack in the housing and after a trip to the Ford store, replaced it with a new one. I wasn't able to install and test it until this morning but when I did, there is now left turn signal at the trailer connector. I don't have the camper at this location to verify it's working but believe it should be. Thanks to all for sharing the great wealth of knowledge that you have. I'll post once the final test has taken place.
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Great to hear!
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