HeadLights Activate Electric Brakes!

[Muskie]

Hi folks, curious situation. I was driving the rig down the road during the day, and I noticed my brakes were not working on my 59 Tradewind. So I wanted to make sure my electrics were working in general, so I put on my lights to test and the brakes locked and I skidded! I immediately turned off the lights and used the tow vehicles brakes. Luckily I was on side roads and close to home, and it was during the day.

Bit of history; I had a new axle and running gear put on a few years back from Colin and my mechanic put it all together including the electrics. It has been working great. I did notice my 7 way plug had corrosion this year from winter weather, so replaced it, wiring it exactly as my mechanic did, took a picture etc just to make sure. Again, it worked for a small voyage, but my second voyage is when the trouble happened.

I took apart the reciever on my tow vehicle and checked the connections, seemed ok, but it could be dodgy? and still the problem happens, my headlights when turned on from the tow vehicle, activate the brakes. Could it be a faulty controller, or one of many things beyond my wheelhouse? My knee jerk reaction is to replace the 7way receiver-end on the tow vehicle.
Thoughts, experiences?

Cheers folks

[GCinSC2]

Muskie,



What is your tow vehicle? If it's fairly modern I'd use it's 7 way wiring diagram and rewire the trailer 7 way to match the tow vehicle. Example my SWAG meter says your TV's running light circuit is now connected to the trailer brake circuit.


Use today’s modern 7 way standard wiring layout.

Gary

[Wazbro]

Originally Posted by GCinSC2

Muskie,



What is your tow vehicle? If it's fairly modern I'd use it's 7 way wiring diagram and rewire the trailer 7 way to match the tow vehicle. Example my SWAG meter says your TV's running light circuit is now connected to the trailer brake circuit.


Use today’s modern 7 way standard wiring layout.

Gary

Great advice. Hate it if your TV breaks down and you need to have your trailer towed and the tow truck driver turns on lights and destroys your tires and then trailer. Then you get stuck with the bill since caused be your nonstandard wiring.

[Muskie]

Thanks, I think I will bring it to my mechanic, hoping he can trouble shoot from experience.
The TV is a 1991 Astrovan that was wired from scratch and hopefully he will make sense of the wiring and do what you mentioned. I am just curious as to why it started in the first place. Thank you

[GCinSC2]

Electrical wiring diagnosis is a bit of a challange even when you're hands on with the project. If the 7 way on both sides is wired correctly then I'd start looking for a pinched or frayed insulation that is allowing the headlight circuit to connect to the brake wire.

If you do not turn the light on does the brake circuit work correctly?

Has the 7 way cable been pinched at the coupler area or anywhere else? I did a repair of a pinched 7 way cable, insulation cut internally could cause crossover connection.

Any relationship to a recent 7 way or brake system related repair? Happened after I did THIS(?)

Gary

[richard5933]

On a similar note, when you rewired the 7-way on the trailer, I'm assuming that you replaced the pigtail back to where the crimp fittings are inside the trailer. If so, is there a change you left a stray strand of wire somewhere? Possibly one strand from the headlight circuit is sticking out and making the short circuit.

There is nothing really complicated in this, so a step-by step testing should get it done. Start with the tow vehicle and make sure that the proper terminals get current at the proper time and that there is no problem there with headlight power showing on the brake circuit.

Then move on to the trailer, including testing things while manipulating the 7-way pigtail in every directly possible all along the cord. Pay attention where the anchors are for the pigtail, as one of them might have pinched a wire too tightly cutting into the insulation.

Keep working back to the junction point for the 7-way cord.

My guess is that if the problem occurred shortly after you replaced the 7-way it has something to do with that work.

[Bill M.]

It sure sounds like you wired the 7 way to the trailer wrong. You have the clearance lights wire going to the brakes. A few minutes with a meter and a head scratch will fix it. Or maybe just the head scratch. Do the clearance lights come on dimly when you activate the brake lever? BFirst check the signal lights and eliminate everything that works correctly. Then look at what is left. Probably just have to switch 2 wires.

[Bill M.]

I would trouble shoot the trailer wiring first using jumper leads from the battery to the ground lead and a positive.

[rvbsmart]

I would suspect that somewhere in the re-wiring, a diagram or picture was interpreted wrong. I would check the turn signals also to make sure they are correct. The terminal for the electric brakes happens to be exactly 180 degrees around from the headlight/running light terminal, so those two may not be the only ones behaving strangely.

[mykytiukr]

At the 7 wire plug on the trailer, remove the cover. That’s the part that you grab when plugging in or unplugging. There is one screw on it somewhere. It will then slide down the wire exposing the connections. Check to see that they are all tight and are where they are supposed to be. Then check the truck at the plug the same way. Most likely the problem is here. Also, in all my years working on big trucks, when something would come in for an electrical issue or just about anything for that matter, more than half the time the problem was where the last person worked on it!

[JCWDCW]

You did say the brakes worked properly at least once
It sounds like the head light - tail light circuit is wired to the brake input on the controller. This could be mis-wring at the pigtail… even though you say you matched the original wiring… I’ve made the mistake myself. OR there might be a strand of wire in the tail light connector in the plug that has crossed over to the brake circuit
Use a 12 v trouble light or volt meter to verify the TV receptacle first. You will need a small load on the brake circuit… like a lamp with a pig tail
Check the power at the receptacle first then match the wiring at the plug.
Doesn’t sound like you will have a problem solving this!
JCW

[RedSHED]

Maybe put a multi meter and check both harnesses (truck & trailer) for a short between running lights and trailer brakes. Then running lights to ground. Corrosion can make shorts more likely.
I'd be a little surprised if it wasn't something like that. Quite possibly in the connector as an earlier post mentioned.

[Dan and Liz]

Do you have a buddy with a 7-pin you can try and if the results are the same. If so it’s the trailer umbilical.