ok, I got a 1992 F150, factory tow prep. had a 7 round pin that I swapped for a 7 blade. had the 4 pin plug under the dash and I bought the plug and play harness that plugs into the truck and into the controller. everything works like it should except the trailer brake signal. no matter the position of the brake pedal the brake signal wire shows voltage, about 11.8 until you press the brakes and then about 11.5 regardless of brake controller settings. I thought it might be the truck and took the blue wire out of the harness, and the controller was still putting out voltage on the blue wire, none a the truck side on the blue wire. tested the wiring and had ground and 12v at the plug, the red wire only shows 12v with the brake pressed so I thought the truck was fine. replaced the controller and same problem. so I checked the truck out better and there is continuity between the brake signal wire and ground while the brake is not pressed, when pressed its gone. removed plug from brake switch and I think it was the light green w/ red stripe that had continuity with ground, and my meter shows 12V probing the 2 wires at the brake switch. now the correct way would be showing 12V probing one wire and chassis ground, other wire should show nothing until brake switch is activated, right?

so how do my brake lights still work just fine?

I did search and read a few threads and saw that my green/red wire does go into the multifunction switch. just confused on how it could be that when the brake lights still work just fine...

 

just looked at the diagram again and see that the green/red comes from the hazard flasher, and the green goes to the multifunction. but my blinkers/hazards all work fine as well...

 

ok, just changed the title up because my headlights weren't working 100%, had to jiggle the multifunction switch to get them to stay on and putting highs on got nothing. so I replaced it hoping that would solve my brake problem but figuring it wouldn't...

and of course it didn't. I know its not the brake switch itself because removed from the system and just probing the wires I get 12V across them.

is there a common place this wire gets damaged and shorted to ground? what route does it take in the truck? anybody have a wiring diagram they could upload of the circuit?

I need to go pick up a travel trailer but cant figure out this dang brake controller problem.

 

Does the brake controller have the LED lite on it. Mine is on anytime the trailer is plugged into it and that's normal. If your just checking for continuity not sure what it would show. Try checking with a test lamp instead of volt meter at the 7 pin trailer plug.

 

I'm slightly embarrassed about the whole thing now. I hooked everything back up and decided to put my meter to the battery test selection so it put a load on the blue wire, and while testing it I pressed the brake pedal playing with the time and gain settings and the led bars on the display climbed like they should, and the speed/max height of the bars corresponded with the settings... still haven't put a load and tested the blue wire for voltage to see if voltage climbs wit brake gain but I'm confident it will

I'm still very confused why the cold side of of the plug on the brake switch acts as a ground when pedal is not pressed then becomes a 12V+ source when pressing the brake... I feel like it should just be a dead wire until energized y the brake switch, but it all works, so what do I know...

 

Your just seeing the ground at the bulbs feeding through the bulb elements. Bad grounds will backfeed and do the stupidest things. I always start with grounds when the lamps are acting up.

 

So then everything is normal, right?

 

Should be.

 

Mad Matt! I am in the process of hooking up a brake controller in my 2007 E150 without trailer tow package. It has the 4 wire flat connector but that's it. In the controller directions it specifically states the green wire w/red stripe goes to ground when the peddle is depressed. The claim this can damage/destroy the controller. I have tested the green wire at the stop switch and it appears to also go to ground upon peddle depression. I have not been able to find a safe place to get the needed stop light switch signal connection to the red wire on the controller. Some of the same directions on line for late 90's fords want the red wire attached at the directional signal harness on the steering column which my vehicle does not have. Where did you finally hook the red wire from the controller?

 

You would get a better response in the correct forum for your vehicle here: 1968-2013 Full Size Vans


FYI.....MaddMatt02 has not been active in this forum since Dec 23 2016.