Trailer Harness Wiring Help
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Trailer Harness Wiring Help
On our 72 I had a 7 pin wire harness with a brake controller installed by a trailer shop last year. I found that when I run the parking lights or headlights a fuse (self re-setting) begins to trip after 15-20 minutes. When this occurs I loose all lights on the truck and trailer. The truck by itself does not do this and it has done it with two different trailers. I have began pulling the bed wiring and searching for a short. Am I tracking right with this or should I be looking else where?
Thanks
Dan
Thanks
Dan
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Originally I was 100% it was the Uhaul trailer (towing it when the problem came up). But the next week it was my travel trailer which does fine with our Dodge. Well track with your suggestion, I just wish the problem was continuous! Intermittent problems can be a PIA to resolve.. :-)
Of the next Riffraff East
Joined: Oct 2004
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From: Concord NC
Probably find a wire with a rubbed place on it that a bump or jar will cause it to short out and trip the fuse. The reason I think it's the trailer, the wires on the truck are hot when the lights are on when the trailer in not hooked up and you have no problems then. One other thing you may want to check before you spend a lot of time would be to replace the resettable fuse. They will get weak and trip under a load, even if there in not a short.
Of the next Riffraff East
Joined: Oct 2004
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From: Concord NC
Originally I was 100% it was the Uhaul trailer (towing it when the problem came up). But the next week it was my travel trailer which does fine with our Dodge. Well track with your suggestion, I just wish the problem was continuous! Intermittent problems can be a PIA to resolve.. :-)
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That had not crossed my simple mind! 
Your 100% on the fuse and logic with the truck wiring. The fuse that is tripping was in the truck when they did the wiring. No telling how old it is.
I'll try that today..
Thanks!!
Your 100% on the fuse and logic with the truck wiring. The fuse that is tripping was in the truck when they did the wiring. No telling how old it is.
I'll try that today..
Thanks!!
Of the next Riffraff East
Joined: Oct 2004
Posts: 8,679
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From: Concord NC
No problem, hope that is your problem. Simple fix, you may have to replace it with a non resettable fuse of the same size. The extra draw from the trailer may be just enough to cause the fuse to trip. Good luck and let us know if that does the trick.
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CO River Rat
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From: Lake Havasu City AZ
Do you lose power to the brake controller also? If so, the shop combined the circuits and you need to put the brakes on a separate circuit with its own breaker.
Steve
Steve
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Post Fiend
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From: Central Florida
Or look at the draw the trailer adds. Your fuse maybe too small for all of the lights on the trailer. Figure the each tail light filament draws about 3 watts, so 6 watts for just the two tails. Then the little clearance lights will pull at least 2 watts each. Add up your draw and divide it by 12 and that will be your current draw.
The short could also be in the connectors. I have rebuilt plenty of them, most manufactures just wrap the bare wire around the screw. If a wire is stripped too far it maybe contacting a ground or grounded circuit. While you have it a part, it would be a good time to use spade terminals on those wires and cover everything with a dielectric grease.
The short could also be in the connectors. I have rebuilt plenty of them, most manufactures just wrap the bare wire around the screw. If a wire is stripped too far it maybe contacting a ground or grounded circuit. While you have it a part, it would be a good time to use spade terminals on those wires and cover everything with a dielectric grease.
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The trailer shop installed 2 breakers. One 30 and one 25 amp near the battery. The breaker I found (25 amp) was in the cab and I doubt the trailer company knew it was there. I'll find out tomorrow. I plan on wrapping the wire ends of the breaker that was tripping and checking the trailer connector to see exactly exactly what this breaker was connected to. The only reason I found it was, when it cycled I could hear it open and close.
Thanks for the trouble shooting ideas, which we'll work through!!!
Dan
Thanks for the trouble shooting ideas, which we'll work through!!!
Dan
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We have the wiring problem fixed!!
There were 2 issues.
1. Running/Tail Lights cutting out after 7-10 minutes of using them.
2. Found later - The emergency flashers would back feed the brake controller circuit. Every time they flashed, the trailer brakes would lock up!
For the first issue - The light duty wiring of the truck could not handle the running (10)/tail lights (2). So we ran a separate light circuit (powered from the battery relay through a 20a circuit breaker) with a 30a relay which is controlled by the rear running lights.
The second was fixed by placing a diode in between the brake switch above the brake pedal and the turn signal switch.
I did find several bad spots in the wires, but none of those fixes corrected these problems. Thanks for your suggestions!!
Dan
There were 2 issues.
1. Running/Tail Lights cutting out after 7-10 minutes of using them.
2. Found later - The emergency flashers would back feed the brake controller circuit. Every time they flashed, the trailer brakes would lock up!
For the first issue - The light duty wiring of the truck could not handle the running (10)/tail lights (2). So we ran a separate light circuit (powered from the battery relay through a 20a circuit breaker) with a 30a relay which is controlled by the rear running lights.
The second was fixed by placing a diode in between the brake switch above the brake pedal and the turn signal switch.
I did find several bad spots in the wires, but none of those fixes corrected these problems. Thanks for your suggestions!!
Dan
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I found the emergency flasher problem when I stopped to help someone who had ran out of gas out on the Parks HWY. Fortunately, I was only moving 5 mph or so when I put the flashers on and felt the trailer lock-up.
The light duty wiring symptom was learned from another site's member who referenced - 1970 Ford Trucks Body Builders Layout Book - This referenced two circuit breakers which are in the stock light switch and are easily trip if the circuit is tapped into for accessories. Combined with what I learned here, the trailer lights pull about 3 amps. Not much, but when I counted the trucks lights (including stock roof lights) there was too much of a power draw.
The shorts were found after I started this thread and following the guidance here.
My trailer shop suggested a new turn signal switch. $70 later, I have a new switch in the garage. I still may install it..
I would really like to do the complete wire harness, but that will have to wait$$
Thanks again for your ideas and help!! They all helped with this puzzle!
Dan
The light duty wiring symptom was learned from another site's member who referenced - 1970 Ford Trucks Body Builders Layout Book - This referenced two circuit breakers which are in the stock light switch and are easily trip if the circuit is tapped into for accessories. Combined with what I learned here, the trailer lights pull about 3 amps. Not much, but when I counted the trucks lights (including stock roof lights) there was too much of a power draw.
The shorts were found after I started this thread and following the guidance here.
My trailer shop suggested a new turn signal switch. $70 later, I have a new switch in the garage. I still may install it..
I would really like to do the complete wire harness, but that will have to wait$$
Thanks again for your ideas and help!! They all helped with this puzzle!
Dan
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