I recently acquired a very small utility trailer and rewired the lighting system as it was very wonky looking. Upon completion I found that the left/right/brake and flashers all worked fine, but not the tail/parking lights. They don’t come on with running lights or headlights.

I am confident the trailer wiring is 100%.

I took some readings with my multimeter at the plug on Flex and found I was getting no voltage on the taillight pin.

The wiring is not factory installed but appears to be a dealer-installed accessory as the receptacle has “Ford” molded into it.

I traced the wire back a ways and found it enters the cabin through a grommet behind the driver-side taillight. Hidden behind that rear corner trim panel is a Ford trailer light module.

I confirmed fuses and relays that mention “trailer” are all good, including the fuse in line with power wire for the light module which is terminated via a ring terminal in the fuse block.

Is there anything else I might be missing? The only two thoughts I have left are:
1: the module itself is bad
2: the brown input wire is not connected wherever it should be connected at.

In order to check the second option I’m going to have to pull off more trim pieces, which I hate doing.

Hoping I’m missing some other option.

No tow pkg on mine (2013 FWD SEL), and my in laws are about 1k miles away en route to LA, so I can't look at theirs (2016 AWD SEL).

Hope its an easy fix.

I've been putting off tearing into ours. Intermittent backup camera inop. Thinking I need to pull the lift gate panel & check the camera plug.
Luckily its been working fine the last few times I've driven it.

quote:

Originally posted by P250UA5:
No tow pkg on mine (2013 FWD SEL), and my in laws are about 1k miles away en route to LA, so I can't look at theirs (2016 AWD SEL).

Hope its an easy fix.

I've been putting off tearing into ours. Intermittent backup camera inop. Thinking I need to pull the lift gate panel & check the camera plug.
Luckily its been working fine the last few times I've driven it.

I have the same issue with the backup camera too… intermittently non-op.

I realize you said it appears not factory installed - Factory will have both the 4 pin and the 7 pin options, so without that you can be sure it is not factory.
Check the connections at the headlight switch on the dash also.

quote:

Originally posted by sigseller2000:
I realize you said it appears not factory installed - Factory will have both the 4 pin and the 7 pin options, so without that you can be sure it is not factory.
Check the connections at the headlight switch on the dash also.

Right, also no option in the settings for sway control. So it is dealer installed for sure.

There is no apparent wiring running up the driver side except for the red wire which goes to the under hood fuse block. It seems all other taps occurred behind the trim panel where the power lift rod is.

Do you happen to know if the Limited AWD Ecoboosts have the oil cooler that came with factory tow option? I’ve seen conflicting reports.

possible corrosion in the pin for the tail-lights, sounds like the module is getting power and that all the other connections are live, perhaps spray some electrical connector cleaner or, if the connector inside the harness moved back it's not making a connection on that circuit,

Run a jumper wire from the car to the trailer harness for that pin, see if you get running lights. If so make sure the pins are fully seated...

Just a shade tree mechanic (and a not very good one at that), but I'd look at the plug itself vs. the wiring. I'd replace that first.

Trailer plugs are prone to corrosion/rust and in a 6 year old vehicle that's where I'd look.

quote:

Originally posted by Gustofer:
Just a shade tree mechanic (and a not very good one at that), but I'd look at the plug itself vs. the wiring. I'd replace that first.

Trailer plugs are prone to corrosion/rust and in a 6 year old vehicle that's where I'd look.

That is a good thought. Maybe I’ll test the wire right before the plug using the “safety pin” method.

So, I punctured the insulation enough on the wire in question to get my multimeter on it just before the plug and confirmed: no voltage. So I can rule out the plug itself.

I took some trim labels off and traced the wires… the 4 wire trailer plug cable goes into a a Ford light module (dealer installed apparently). The label of the module says the tail lights are differed by the brown wire input to the module. I traced that brown wire to a tap in the driver side taillight bundle. Testing at the tap reveals voltage as expected.

So, the input side to the module is working. The output side is not.

The label on the module also said that if there was a problem with no output from the module to pull the fuse in the power line (which is homeran to the distro block) for 20 seconds and replace.

I did this with mixed results…

The tail lights started working on the trailer!!

But the rest of the lights, which had all previously worked, no longer worked. Brake lights, turn signals, and flashers are all non-op on the trailer (but fine on the car).

So, if that isn’t proof that God has a sense of humor I don’t know what is.

I’ll try another reset via pulled fuse, but it seems like the module itself is wonky and probably needs replacement.

considering the problems, and you need to trailer safely, not to mention the cost of a ticket a new module might be the best route for peace of mind.

A lot of yabo's here with lawn trailers that have zero or partial lights working...

quote:

Originally posted by HRK:
considering the problems, and you need to trailer safely, not to mention the cost of a ticket a new module might be the best route for peace of mind.

A lot of yabo's here with lawn trailers that have zero or partial lights working...

Yea, if a final check for short circuits on the trailer side and a reset via fuse-removal fail to reveal the problem, I think I’ll just replace the module or remove it and use an aftermarket replacement. Those are plug and play and would take far less time to install than I've already spent on it.

https://www.etrailer.com/t1-2016_Ford_Flex.htm


MIght help, video there, a little research shows a 7 pin and 4 pin option, the video goes through both..

A google search shows many many issues with Ford's trailer light module.

I paid a guy to put a trailer hitch on my Ford Flex two years ago... took 30 minutes to put the trailer hitch on... 2 hours to do the wiring harness... good luck.

How are the trailer lights grounded? It sounds like you may have a grounding issue.