# Trailer Light Question



## sdgoosehunter16 (Sep 22, 2009)

Just a quick question...ive got an old pickup box trailer(anything a hs student would need) but i bought some lights to put on the back of it to make those dark mornings a little brighter however when i hooked them into the power source of the trailer coming from the truck the tail lights just dimmed and the lights never turned on?! any ideas would be great!

Thanks, 
Tanner


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## rmc_david (Sep 23, 2009)

Tanner,
First and foremost, lets try to find out if you vehicle has a negative or possitive ground system. If you have a possitive ground system, then you are likely encountering a simple issue of an incapability of the lights you have installed with your wiring system of the vehicle it is connected to. Secondly, make sure you have a sufficient ground between the trailer and the vehicle in which it is connected. Last, but certainly not least, lets make sure your lights aren't designed for a current greater than that which your vehicle will supply. Simply put, make sure your lights are designed to operate on 12V DC and not 120+V AC.
If none of this helps, let me know and I'll see if I can research it a little more for you.


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## Horker23 (Mar 2, 2006)

Did you hook the extra lights up to your running lights or a constant 12V feed. If you hook them up to your running lights this will happen as you do not have enough power to support all those lights. Also check your wiring because some light sould come out of you extra lights when the others dim.


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## JBB (Feb 9, 2005)

Check your ground wires. Try to run a seperate ground wire from the truck to your lights when you power up your lights and see what happens. If it works great if not run a seperate power wire to the lights(with a fuse in the line).


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## Horker23 (Mar 2, 2006)

What would a extra ground do? You can just ground the lights at the back of the trailer with a selftapping screw.


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## wingaddict (Sep 16, 2009)

its more than likely the ground. but the big question is. where did you hook up the ground wires coming off the lights ? most lights have short ground wire that is designed to be screwed to steel, or something else that will give you a good solid ground.

also make sure you have the hitch hooked up to the pickup when your testing this. sometimes a trailer wont ground itself and has to be hooked to the vehicles ground (via the hitch)

If you have an aluminum topper or something on the pickup box that you are mounting the lights to, you wont get a good ground to the box trailer itself. If thats the case run a longer gorund wire directly to the metal of the pick up box.
That said, you shouldnt try to run flood lights off the existing wiring of the trailer the wiring(probably 16g) isnt designed to run that much power.

You should be running a seperate power source from the truck to the trailer for lights, not just tapping into the running lights off the trailer.


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## JBB (Feb 9, 2005)

Honker 23 wrote

What would a extra ground do? You can just ground the lights at the back of the trailer with a selftapping screw.

The biggest problem with trailer lights is the ground between the truck and trailer. I have only been a mechanic for 38 years so my experience is a little limited. 
If lights dim when turning on other lights that tells you that the light you just turned on is trying to find a ground thru the other lights.


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## Horker23 (Mar 2, 2006)

Or not enough power to light them up!


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