Trailer wiring question? - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 5 (permalink) Old 07-30-2006, 03:54 AM Thread Starter
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Question Trailer wiring question?

I have a JMH dump trailer and I need to put a back up alarm on the trailer. How do I wire it so it will come on when I am in reverse? The tractor already has one.
The frame is a 1979 East and the JMH body is a 1997.
Thanks.
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post #2 of 5 (permalink) Old 07-30-2006, 12:43 PM
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Quote:
Originally Posted by Truckie
I have a JMH dump trailer and I need to put a back up alarm on the trailer. How do I wire it so it will come on when I am in reverse? The tractor already has one.
The frame is a 1979 East and the JMH body is a 1997.
Thanks.
I'm not a wiring expert, but I think the hot wire gets spliced into the trailer's reverse lights (if the trailer has them) and the ground wire would just be mounted to the frame.
If your trailer doesn't have back-up lights, then you'd have to run a wire from the back-up alarm up the the front of the trailer to its' wiring plug and find the wire in the plug that is hot when the truck is in reverse. You'll find out which terminal is hot in the truck's trailer wiring socket by turning the key to the ign. position with the truck's tranny in reverse (truck's engine is OFF, but electrical system is ON). Once you determine which terminal is hot with the truck in reverse, you can determine which terminal in the trailer plug will be hot when the truck is in reverse. Install the wire from the back up alarm to that terminal in the trailer's wiring plug so when you shift into reverse, it makes the back up alarm work.
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post #3 of 5 (permalink) Old 07-30-2006, 02:43 PM Thread Starter
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Quote:
Originally Posted by Duke
I'm not a wiring expert, but I think the hot wire gets spliced into the trailer's reverse lights (if the trailer has them) and the ground wire would just be mounted to the frame.
If your trailer doesn't have back-up lights, then you'd have to run a wire from the back-up alarm up the the front of the trailer to its' wiring plug and find the wire in the plug that is hot when the truck is in reverse. You'll find out which terminal is hot in the truck's trailer wiring socket by turning the key to the ign. position with the truck's tranny in reverse (truck's engine is OFF, but electrical system is ON). Once you determine which terminal is hot with the truck in reverse, you can determine which terminal in the trailer plug will be hot when the truck is in reverse. Install the wire from the back up alarm to that terminal in the trailer's wiring plug so when you shift into reverse, it makes the back up alarm work.
Ok I follow you pretty much on what you said. So basically I just need to put the truck in reverse with the engine off and get out my test light, and see which wire is going to be hot in the pig tail while in reverse and find that in the plug hole on the trailer and tap that. Correct?
Thanks.
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post #4 of 5 (permalink) Old 07-30-2006, 03:34 PM
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Originally Posted by Truckie
Ok I follow you pretty much on what you said. So basically I just need to put the truck in reverse with the engine off and get out my test light, and see which wire is going to be hot in the pig tail while in reverse and find that in the plug hole on the trailer and tap that. Correct?
Thanks.
Exactly. I wasn't sure if you had back up lights in your trailer. Some do, some don't.

If you have them, then just tap into the back up light wire for the power side of your alarm.
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post #5 of 5 (permalink) Old 08-05-2006, 11:35 AM Thread Starter
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Well I checked the pig tail like you said to do and no luck. The only hot pin is the center pin, which is for trailers that have abs brakes. I donít have reveres lights on the trailer. So I guss I will just keep the one on the tractor.
Thanks for the help.
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