Towing harness issue SOLVED!

Fellas Im stumped. Ive eliminated the problem is the truck itself and not the trailer by using a test plug.

Background: 2012 DCOR with factory towing package and all factory lighting. I once put in junction block/flasher relay to disable the DRL, but after finding out 2012+ integrated the towing converter relay into the DRL system, I put everything back to stock configuration.

Problem: Truck brake light and signal works. Trailer right brake and signal does not.

Testing: I've removed and replaced all known fuses/relays that tie to the towing harness. There's power to the harness, just not the right brake and right signal. However, when I hit the factory alarm to lock the doors, the test plug would light up, indicating there's power to the plug (both the left and right turn signal).

Is there hidden fuse/relay that im not aware of? I've checked the ones in the engine bay and the ones by the kick panel.

Thanks

 

This is a bit over my head?
My guess would be that the Wireless Lock / Alarm uses the Hazard circuitry.
And the Stop/Turn uses the Turn Signal?

The strange part is the Stop light doesn’t work?

Looks like this is a something for @caribe makaira to take a look at.
I’m stumped too

 

The hazard switch would light up the left signal but not the right.

Forgot to add, the right side gets power because when headlights are on, the right side is on. Just no signal and no brake. Flashes with door locking and unlocking.

 

Any time I run into a problem like this on other people's trucks, the very first thing I check is how solid the grounds are, both on the truck and on the trailer. By that I mean truck ground connector to truck frame, and then (separately) trailer ground connector to trailer frame. Also check resistance between trailer frame to truck frame while the connector is plugged in. And don't go by just appearance; use an ohmmeter and look for a reading that's way down in the 0-5 ohm range (use the meter's X1 range). You will have to extend your test leads by many feet to perform these tests. Don't forget to check for nice clean metal on all plug contacts. If they look even slightly brown, hit them with a good dose of electrical contact cleaner and NOTHING ELSE.

Something else I've run across on 7-way connectors is people mating differently-wired connectors, that is, a 7-way "traditional" mated with a 7-way "RV standard."

Also verify no wires in the harness are abraded/shorted to ground or each other, from the controller all the way back through the mating connectors and through the trailer frame.

I've seen some truly awful wiring hack jobs, once by a very well-known truck conversion firm on a brand-new F350 diesel. That incident was when I decided never to trust anything again, and never again assume the wiring is okay.

 

Yeah, that’s what is confusing.
Both use the Flasher relay as far as I can tell?
caribe makiare can probably figure it out?

 

Locking and unlocking the door activates the right turn signal lead in the harness, just not from turn signal stalk nor the hazard switch. Would that eliminate the possibility of a bad ground?

 

Yes, you would think the ground is good if the other lights on the trailer work.
You could easily test it by checking it with a DMM.
Go from Ground to R/H Stop with a DMM or Test Light.

 

Have you inspected and actually tested the connections with a test light or just the test plug? I know the results are likely the same, but it is hard to beat poking around with a 12v test light probe.

 

You'll drive yourself crazy trying to find the source of the problem by looking at the symptoms. Get out the ohmmeter and check the integrity of your grounds, and make sure nothing's shorted (or open).

 

No test light was used. I've tried 2 different trailers, swap light bulbs, swap fuses with working ones... With the test plug I can safely say the trailer isn't the issue but the truck itself.

 

Yea I'll do that this week. I was actually going to my parents to grab my ohmmeter when locking the door of the truck triggered the test plug light. I jumped to conclusion there's a proper ground since that worked.

 

Keeping just the affected circuit in this drawing (omitted the vehicle turns) The relay combines the stop and turn to one wire.
Tail/Parking has its own wire.
I'd say you have a failing relay.

 

Im not gonna lie, there were times during towing when I hit the brakes there's a burning smell coming from the dash area. I couldn't find anyone with this "burning smell while towing" issue. Wonder if it has to do with the failing relay.

 

Do you have a Towing - Brake Controller?

 

No I do not. My small boat trailer doesn't have brakes.

 

Well, then I check the flasher relay.

 

Thanks guys for all your help. I'll give it a look and report back my findings.

 

caribe makaira, thanks for leading me to the problem.

I ordered a new turn signal flasher, 81980-04050.

I took apart the new one and the old one to compare, the old one is sorta burnt and the chips are shifted. I assume it's a bad flasher from the factory? I can't imagine anything can cause that to happen.

Back to normal functioning tow harness. Thanks guys.

 

You mentioned that you have the factory tow package. I’m curious if it really is, or if it’s a dealer installed tow package. Do you have the engine oil cooler?