classicJackets (FS)
classicJackets (FS) Dork
11/5/21 10:33 a.m.

Alright guys, fun problem to solve here. My 2000 Expedition came to me with a hitch and 4-pin connector installed. Everything always has worked fine. 

Prior to the challenge, I had a shop upgrade me to a 7-pin to mate up to the trailer I was borrowing, and add a brake controller. Everything worked well when I picked the car up, and (as far as I know) until earlier this week.

What happens now: 

 

With no trailer: Turn signals have the "fast flash", and fronts work. No rears. No brake lights, but the Brake Controller "sees" when I'm on the brakes. Running lights work.

With Trailer: Trailer brake lights and turn signals work, but the car still has no brakes/turn signals. No "Fast flash" on the dash. Running lights work.

 

Our drive home was 14 hours through the rain, which may or may not have an impact. 

All fuses are intact. The wiring for the 7 pin is pulling brake/turn signals from the original wiring for the 4 pin. Grounds are solid. What am I not thinking to check (other than bulbs)?

Jesse Ransom
Jesse Ransom GRM+ Memberand UltimaDork
11/5/21 10:49 a.m.

Sounds like a wiring diagram will need to be consulted.

I'd be looking for something shared by the rear brake/turn lights. And I gotta say that sounds like a ground.

It seems reasonable that if the same signal is being patched through to the trailer and it has a functioning ground for those lights, then it becomes surrogate rear lights and the fast blink stops, etc.

When you say running lights work, does that include non-brake taillights? I'm not sure, but would think those would use the same ground, which makes things weirder.

GRM is an astonishing collection of specific knowledge and maybe someone has seen exactly this on this vehicle, but I'd be looking for that diagram...

Kendall_Jones
Kendall_Jones Dork
11/5/21 11:47 a.m.

bulbs burned out.  Fast flash with nothing connected means the overall resistance is low - which means bulbs are burned out (open).  I'd check the bulbs...

Toyman01 + Sized and
Toyman01 + Sized and MegaDork
11/5/21 12:00 p.m.

The trailer wiring T adapter is probably unplugged under the back of the vehicle. It splices the trailer wiring into the rear lighting harness at the plug. At a guess, the truck lighting side is loose.

Probably looks something like this. 

Amazon.com: CURT 55301 Vehicle-Side Custom 4-Pin Trailer Wiring Harness,  Fits Select Ford F-150, F-250, F-350 : Automotive

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
11/5/21 12:44 p.m.

Sounds like something with the truck.

Those years of many of the trucks (including Ford) have separate circuits with their own fuses for the trailer lighting.  Those circuits are still controlled by the flasher/BCM in the truck, so my guess is that you have ground, bulb, or socket issues in the truck.  Once the trailer is hooked up, the BCM/flasher sees a resistance/load that it can work with and it operates normally even without the truck lights.

Also possible that the shop messed with something they shouldn't have, although a smart shop would just buy the plug n play adapter.

The brake controller sources from the brake light switch on the pedal, so it can function on its own regardless of whether or not the brake lights actually illuminate on the truck or trailer.  All it sees is a 12v signal from the switch, then uses G-forces to control the braking.

classicJackets (FS)
classicJackets (FS) Dork
11/11/21 1:10 p.m.
Kendall_Jones said:

bulbs burned out.  Fast flash with nothing connected means the overall resistance is low - which means bulbs are burned out (open).  I'd check the bulbs...

Somehow this was the right answer. I thought it was too much of a coincidence to lose them both at once, but here we are -2 new bulbs and I'm back in business

Robbie (Forum Supporter)
Robbie (Forum Supporter) GRM+ Memberand MegaDork
11/11/21 1:48 p.m.
classicJackets (FS) said:
Kendall_Jones said:

bulbs burned out.  Fast flash with nothing connected means the overall resistance is low - which means bulbs are burned out (open).  I'd check the bulbs...

Somehow this was the right answer. I thought it was too much of a coincidence to lose them both at once, but here we are -2 new bulbs and I'm back in business

Just means that bulb supplier was exceedingly accurate at hitting their service life spec established by ford. haha. 

Jesse Ransom
Jesse Ransom GRM+ Memberand UltimaDork
11/11/21 5:50 p.m.

Glad it's fixed. I kinda love/hate stuff like this. Great reminder that even if it looks weird, you gotta start with the basic/easy.

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