Trailer Blinkers/Lights Troubleshooting

Evan B

Evan B

Bobber Downey Jr.
Staff member
Admin
**update: issue resolved

So I'm running out of ideas here. I have a 2013 F150 FX4 and my trailer running lights are working, but not the blinkers. And no, it isn't on the boat side. I have two boats/trailers, and both are doing the same thing. I also have a testing light plug showing no signal on the blinkers.

The obvious fix for this seemed to be replacing the fuse/relay shown here:

1717101215944.png

So I did that, but no dice. Still nothin. The only other thing in the fuse panel that could be it are two relays shown below. I just don't see how I'd have a double failure at the same time (37 & 38):

1717101272691.png

Anyone have any other awesome ideas? Towing my boat from Gresham to Newport for halibut tomorrow evening and hoping to not white knuckle it every time I turn.
 
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You likely have already done this, but YouTube has been helpful solving some odd issues to me on various things.
Besides here, you might also find some fix suggestions on the F-150 forum.
Good luck with the fix!
SF
 
Do you have brake lights...and will the turn signals work when you brake ?
Evidently...it's a thing with some Fords.
Assume you towed with it before w/ no problems .
 
Evan B said:
So I'm running out of ideas here. I have a 2013 F150 FX4 and my trailer running lights are working, but not the blinkers. And no, it isn't on the boat side. I have two boats/trailers, and both are doing the same thing. I also have a testing light plug showing no signal on the blinkers.

The obvious fix for this seemed to be replacing the fuse/relay shown here:

View attachment 116273

So I did that, but no dice. Still nothin. The only other thing in the fuse panel that could be it are two relays shown below. I just don't see how I'd have a double failure at the same time (37 & 38):

View attachment 116274

Anyone have any other awesome ideas? Towing my boat from Gresham to Newport for halibut tomorrow evening and hoping to not white knuckle it every time I turn.
Click to expand...
If relay 23 or 39 are the same style relay I would swap those over to 37/38 to verify it's not the relays really quick. Otherwise you're going to have to start probing with a multimeter and work your way from the junction box back to the trailer plug.

I found what should be the right wiring diagram. You can remove the relay and probe where Pin 3 goes for both of those relays and you should always have power there being fed by fuse 73. Pin 1 for either relay should get power when brakes or turn signals are on. Pin 2 you can check for ground, it should have continuity with ground close to 0 ohms when probed. Both relays share the same ground so could be a possibility there. If you have power at pin 3, you could jump pin 3 and 5 to bypass the relay and check to see if you are lighting up at the test plug. If power and grounds check out at the junction box, you're going to probably have to start tracking down the connectors between the junction box and the plug at the back bumper to find where the power stops.

trailerwire-1.png
 
Is this one of those cases where when a relay is replaced, it needs to be re-programed, or its firmware updated? I'm told that with modern vehicles we're no longer driving a car or a truck, but rather we're driving 40 or 50 computers around, leaving me lost before I get started.
 
Are your trailer brake lights working?
 
I hate trailer lights. That said you should make an additional ground and connect it from the truck to the trailer. Alligator clips are sufficient. Just makes sure it's all clean. Ground is generally weak for trailers and the ball at the beginning of the season is often rusty and unclean resulting in bad ground. I have one trailer that functions similarly to yours unless I use the additional ground wire. With this it functions perfectly.
 
it's gonna be this i'm sure (answer around 12min in)

 
I had a similar problem with my forester, and the problem was corrosion where the car side plug attached to the cars wiring harness.
 
I'm happy to report that cutting off that old wiring harness and wiring in a temporary flat four adapter has solved the issue. Happy it was just that ☺

Given my super small time available to get this ready before I go, I appreciate all the ideas here.
 
Evan B said:
I'm happy to report that cutting off that old wiring harness and wiring in a temporary flat four adapter has solved the issue. Happy it was just that ☺

Given my super small time available to get this ready before I go, I appreciate all the ideas here.
Click to expand...
Sweet!
 
Evan, I’ve definitely had the truck side plug wear out. My Silverado was used when I bought it from a small landscape outfit and it had been plugged into so many times it’s was wore out.
 
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