Help! Trailer Brake/Electrical Problem

[Lin in NC]

I have a new FGRV, lightweight only 2100 pounds. Have pulled it twice and used trailer brakes with no issues.

Today I hooked it up and drove approximately 1/2 mile...smoke began to fill the passenger compartment of my truck. Immediately turned off engine and popped the hood. Wiring had melted in the engine compartment as well as wiring at the harness/7 prong connector at rear of truck.

I had the truck towed to dealer...they will be looking at tomorrow.

Any ideas of what may have caused this. I'm at a loss. Any help will be appreciated.

[Francesca Knowles]

I'm puzzled by your reference to the brakes- is there some reason to suspect a malfunction in that part of the sytem? Since the burnt wires were in the engine compartment as well as at the rear hookup, I'd be more inclined to suspect the trailer battery charging line if there is one.

If such a line is present, you might check the condition of the trailer batteries- a malfunction/power surge in that line should cause the fuse at the battery to blow.

If there IS a fuse at the battery, of course.

Francesca

[Frederick L. Simson]

Originally Posted by Francesca Knowles

I'd be more inclined to suspect the trailer battery charging line if there is one.

Unless you were braking at the moment the smoke started...
Either the Battery Charge line (Black Wire) or the Brake line (Blue Wire) shorted to Ground (White Wire).

[Lin in NC]

Originally Posted by Frederick L. Simson

Unless you were braking at the moment the smoke started...
Either the Battery Charge line (Black Wire) or the Brake line (Blue Wire) shorted to Ground (White Wire).

I'm a newbie to this so help me out a little further....I was under impression that trailer battery was not connected in any way with trailer brake system. Thought that all electrical power to braking system came thru the brake controller and controlled by electrical system in the truck. If I am interpreting this correctly are you saying
that there could have been a problem with the trailer battery/electrical system that may have caused this? Thank you and I apologize for these basic questions

[Ron in BC]

No, you're correct, the power to the brakes comes from the tow vehicle battery to the controller then to the trailer.

However, all wires go through the 7 pin connector. Some broken insulation from chaffing or anything that would allow a short circuit would cause this situation. The brake wire only has current flowing when the brakes are on.

The most likely cause is a short circuit, which as Francesca notes, should have blown a fuse, not caused melted insulation.

[Lin in NC]

Originally Posted by Ron in BC

No, you're correct, the power to the brakes comes from the tow vehicle battery to the controller then to the trailer.

However, all wires go through the 7 pin connector. Some broken insulation from chaffing or anything that would allow a short circuit would cause this situation. The brake wire only has current flowing when the brakes are on.

The most likely cause is a short circuit, which as Francesca notes, should have blown a fuse, not caused melted insulation.

This is very helpful. I will be talking with the truck/auto dealer tomorrow morning that installed the brake controller and wiring and my fear was they were somehow going to blame it on the trailer (which I have towed without incident until this morning). Appears the wiring between truck battery/brake controller/7 prong connector may be the culprit. I do not think they installed a fuse in the circuit.

Thanks for the feedback. Any further thoughts are certainly welcome

[Roy in TO]

Nice diagram on connector wiring here:
Trailer BackUp Lights Wiring ? - F150online Forums

[Byron Kinnaman]

Very few, but some 7 pin connectors can be plugged in upside down, even partially plugged in can cause what you described. Wiring doesn't just go bad or suddenly miss-wired.

When one plugs the trailer into the tow it's always a good idea to check the lights, turn and running lights.

[Thinh]

As my understanding, brake wire which comes out from brake controller will be positive when TV brakes are applied, and this wire usually doesn't go thru a fuse unless one installs it as extra caution. About 7-pin connector, there is only one wire(usually Black) is connected directly to positive terminal of TV's battery. Given to the fact of burning wires in engine compartment and in 7-pin harness, I doubt about they all are burnt. If brake wire(blue) is burnt, it could be shortened(touch the frame/ or one of trailer brake magnet has it's coil shortened) then only this blue wire is burnt, not others. If the black wire(auxiliary + 12VDC) is shortened, the TV's battery fuse would be blown and again, no other wires would be burnt....One more thing, if the brake controller module is dead or blown, I doubt about any blown fuse from TV battery or electric brake line would be melted....IMO, the melting of all wires in 7 pin harness belonged to TV plus portion within engine compartment could only happens when there is a short circuit of black wire(+12VDC) from towing vehicle and this wire has no fuse at all when connected directly to towing vehicle's battery. Again, nothing is mentioned about trailer, so I would think trailer battery/circuitry wouldn't play any role in this phenomenon. Hoefully other inputs or the shop will give better answer.

[Lin in NC]

Originally Posted by Thinh

As my understanding, brake wire which comes out from brake controller will be positive when TV brakes are applied, and this wire usually doesn't go thru a fuse unless one installs it as extra caution. About 7-pin connector, there is only one wire(usually Black) is connected directly to positive terminal of TV's battery. Given to the fact of burning wires in engine compartment and in 7-pin harness, I doubt about they all are burnt. If brake wire(blue) is burnt, it could be shortened(touch the frame/ or one of trailer brake magnet has it's coil shortened) then only this blue wire is burnt, not others. If the black wire(auxiliary + 12VDC) is shortened, the TV's battery fuse would be blown and again, no other wires would be burnt....One more thing, if the brake controller module is dead or blown, I doubt about any blown fuse from TV battery or electric brake line would be melted....IMO, the melting of all wires in 7 pin harness belonged to TV plus portion within engine compartment could only happens when there is a short circuit of black wire(+12VDC) from towing vehicle and this wire has no fuse at all when connected directly to towing vehicle's battery. Again, nothing is mentioned about trailer, so I would think trailer battery/circuitry wouldn't play any role in this phenomenon. Hoefully other inputs or the shop will give better answer.

Thanks to all on this forum for the information. I should now be better prepared to discuss with the shop. Am hopeful that only damage is to wiring harness to trailer and no extensive damage to vehicles electrical system

[Ron in BC]

Originally Posted by Thinh

, and this wire usually doesn't go thru a fuse unless one installs it as extra caution.

The power for the brakes should go from either the battery terminal to a fuse to the controller or from a fused terminal in the fuse box.

In no case should an unfused hot wire be used. If it shorts out then it melts insulation and could cause a fire and loss of the vehicle.

Running an unfused hot wire is not acceptable and you should confirm that the shop that installed the controller connected it with a fuse. A fused line is not an option.

[Thinh]

Originally Posted by Ron in BC

The power for the brakes should go from either the battery terminal to a fuse to the controller or from a fused terminal in the fuse box.

In no case should an unfused hot wire be used. If it shorts out then it melts insulation and could cause a fire and loss of the vehicle.

Running an unfused hot wire is not acceptable and you should confirm that the shop that installed the controller connected it with a fuse. A fused line is not an option.

You are correct in term of electric brake lines belonged to trailer camper, not in TV, IMO. In towing vehicle, at brake pedal SW, there is a connector with 4 pins usually. One of the pin is permanently hot +12VDC and another will be hot when brake pedal is depressed. This wire will be led to brake lights of TV, also to the input of brake controller. It has fuse in TV fuse panel. Again, the blue line for electric brake of trailer which goes into 7pin connector of TV also comes out from brake controller outputs. This brake controller module is powered by TV's battery, also protected by TV battery's fuse. That is why this line goes from (blue, usually) brake controller output to 7pin connector of TV without any fuse,(not necessary). That is my understanding, I could be wrong though.

[Roy in TO]

Did a quick search for Tekonsha wiring diagrams. Came up with this one from etrailer for the Voyager controller. Interesting enough that it shows two circuit breakers and no fuses. It appears to want a 20A breaker between the battery and controller, with the 40A breaker between the battery and 12V positive.

[Lin in NC]

Originally Posted by Roy in TO

Did a quick search for Tekonsha wiring diagrams. Came up with this one from etrailer for the Voyager controller. Interesting enough that it shows two circuit breakers and no fuses. It appears to want a 20A breaker between the battery and controller, with the 40A breaker between the battery and 12V positive.

Thanks to all for the feedback. Dealer found the problem today. Wiring harness was routed too close to parking break. Constant movement of parking brake wore thru one of the wires causing a short. The hot wire was fused but fuse did not blow out. Dealer believes that fuse was too high an amperage. Dealer installed new wiring and lower amperage fuse at no cost to me. No damage to trucks electrical system. Alls well that ends well

[Francesca Knowles]

Whew!

I hope to shout it was "no cost to you"- since it sounds like they made the mistake to begin with.

Good reminder for folks to check routing of such work- I had something similar happen, though no malfunction as a result. In my case, a few days after I had the tow wiring done I happened to notice a big ol' wire hanging down almost to the ground under the car.

Turns out one of the lines went from back to front without any support or effort to conceal/protect it. You may be sure I'm much more vigilant about checking such work now...

Francesca

[Thinh]

Originally Posted by Roy in TO

Did a quick search for Tekonsha wiring diagrams. Came up with this one from etrailer for the Voyager controller. Interesting enough that it shows two circuit breakers and no fuses. It appears to want a 20A breaker between the battery and controller, with the 40A breaker between the battery and 12V positive.

...An auto-reset breaker in a circuit plays roles of both breaker and fuse and it is reset-able, as my understanding...

[rabbit]

Great thread.

Jack

[Roy in TO]

Originally Posted by Thinh

...An auto-reset breaker in a circuit plays roles of both breaker and fuse and it is reset-able, as my understanding...

Fuses are only good for one bad event and have to be replaced.
Breakers are good for more.
Some you have to manually reset.
Auto-reset, keep resetting themselves. So fast, you can hear them "buzz".

[David B.]

Originally Posted by Lin in NC

I have a new FGRV, lightweight only 2100 pounds. Have pulled it twice and used trailer brakes with no issues.

Today I hooked it up and drove approximately 1/2 mile...smoke began to fill the passenger compartment of my truck. Immediately turned off engine and popped the hood. Wiring had melted in the engine compartment as well as wiring at the harness/7 prong connector at rear of truck.

I had the truck towed to dealer...they will be looking at tomorrow.

Any ideas of what may have caused this. I'm at a loss. Any help will be appreciated.

I'm glad the cause was found, and I enjoyed the brainstorming of causes to look for if this happens to us. Here in the desert of Arizona we have trouble with rodents chewing wires and causing all kinds of electrical problems.
Happy Trails
Dave & Paula

[Roy in TO]

Originally Posted by David B.

Here in the desert of Arizona we have trouble with rodents chewing wires and causing all kinds of electrical problems.

We've got the same thing up here in Canada. Just this week, I had a squirel strip the insulation off clean to about 8" of wire to a light under the eaves where she was building a nest. I lost 3 rooms inside, when I unknowingly flicked the switch. Hope she had a shocking experience.