Trailer wiring question
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Trailer wiring question
Whenever I put my 93 F-150 in reverse, the brake lights on the trailer come on. It's done this with every trailer I've pulled, so it's not faulty trailer wiring. It has a plug-in harness, so I don't see how it could be wired wrong. Are some kits just set up this way? The harness was installed by a previous owner, so I have no information on it. Could this be a short? It doesn't necessarily bother me that the brake lights come on in reverse, I'm just concerned it may cause other problems (short something out etc.). Any ideas? Thanks in advance.
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From: Southern California
Trailer wiring question
I was thinking maybe the PO hooked a jumper between the truck's backup lights and the brake light connection in the plug. But if that were the case, I think the backup lights would come on every time you stepped on the brakes. But there must be some sort of cross-connection on the trailer plug. Look for a wire spliced into the backup lights and follow where it goes.
Scott
Scott
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Trailer wiring question
Thanks for the reply, Scott. I can't find any wires that have been spliced or anything that looks out of the ordinary. Like you said, if the two circuits were connected, the back-up lights should come on every time I hit the brakes. I'm stumped by this one. I guess I'll just leave it alone & hope it doesn't cause any problems. Thanks again.
Senior User
Joined: Oct 2002
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From: Fayetteville (Atlanta) GA
Trailer wiring question
Well looking at the wiring diagrams I don't see how this is happening. With the trailer connected to the truck do all the other lights on the trailer work correctly? Right and Left turn signals ? Brake lights ? Running lights ? What do they do when you have the running lights ON, and say a right turn signal. Do you have the correct part number light bulbs in the truck and trailer? Grasping at straws here !
Mark
Mark
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Trailer wiring question
Time for the stupid question.
Have you verified that the trailer brake lights come on when the truck brake lights come on?
Do the turn signals on the trailer work correctly?
If all else fails, verify that you are getting a good ground from trailer to truck. I've seen a bad ground cause all sorts of unusual problems.
Have you verified that the trailer brake lights come on when the truck brake lights come on?
Do the turn signals on the trailer work correctly?
If all else fails, verify that you are getting a good ground from trailer to truck. I've seen a bad ground cause all sorts of unusual problems.
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New User
Joined: Feb 2003
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From: MN
Trailer wiring question
I had this same problem on a 91 F150 plus I was blowing fuses the fix was to cut the white Ground wire and tape it up from the wire harness and ground the other end to the frame (plug on Truck)
Hope I explained this OK?
Tlukes
Hope I explained this OK?
Tlukes
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Trailer wiring question
Thanks for all the replies. I don't actually own a trailer myself, so I can't do much testing right now. However, I do have a hitch-mounted brake light that plugs into the trailer harness, so I tried a few things with this. The only new info I found was that with the truck in reverse, the brake light was on (only the plug-in light, not the ones on the truck), but when I turned on the emergency flashers, the light flashed with the flashers. It burned steady when I used the turn signals. I know I need to hook to a trailer to get complete info, but I thought I would share what I found. I guess I need to look into the ground as some of you suggested. By the way, when hooked to a trailer, everything works properly (running lights, brake lights, turn signals, emargency flashers) except when I shift to reverse. Thanks again.
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From: Southern California
Trailer wiring question
Well if your hitch light show's the turn signal's are coming in solid instead of blinking that may tell you something. Most trailer lights have two-element bulbs with one element used for tail lights and the other shared for brake lamp and turn signals.
I think you're going to have to get a voltage tester or a 12 volt light and check the individual pins on your truck's connector. One of them should be a ground. Once you test the pins, you may still need to trace the wires back to the source. It still sounds like something is cross-wired or the ground connection has been substituted for something else.
This link may help with some info on the plug.
Scott
I think you're going to have to get a voltage tester or a 12 volt light and check the individual pins on your truck's connector. One of them should be a ground. Once you test the pins, you may still need to trace the wires back to the source. It still sounds like something is cross-wired or the ground connection has been substituted for something else.
This link may help with some info on the plug.
Scott
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Trailer wiring question
I was unclear in my previous post. With just the turn signals on, the hitch light did nothing, but in reverse, the hitch light burned steady with or without the turn signals on. I will try to find a trailer to hook to so I can diagnose the problem better. I really appreciate everyone's patience & input. I know this is hard to troubleshoot without seeing it first-hand.
Hotshot
Joined: Feb 2003
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From: Long Beach, Ms.
Trailer wiring question
The easiest test I can think of is to pull into a RV dealer or trailer sales and ask them to plug in thier system tester. Most places will do this gladly and for free. You do have something crossed up as a 4 pin carries left turn/ brake-right turn/brake- running lights& ground. Try this url http://www.etrailer.com/faq/wi...
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