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Any harm in hooking up trailer lights backwards? #5237501 10/11/19 11:07 PM
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motor_oil_madman Offline OP
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So apparently I don't pay attention to how things go together like I used to. Then again I didn't count on not being able to decipher the color of the wires on my trailer. They were painted black and even after removing the paint the colors are about the same. Is there any harm in hooking up the brake like wire to the running light bulb accidently if I have them backwards? The other issue is I have a ground issue where the lights only seem to ground through the trailer hitch ball even though I grinded the paint down to bare metal on the tongue and both tail lights.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5237507 10/11/19 11:38 PM
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only if the trailer brakes come on with the lights.....

Re: Any harm in hooking up trailer lights backwards? [Re: tundraotto] #5237513 10/11/19 11:50 PM
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motor_oil_madman Offline OP
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Originally Posted by tundraotto
only if the trailer brakes come on with the lights.....


I got ya. The brakes would be on the entire time the running lights are on. This trailer has no brakes anyways. Obviously I'm going to switch them around if I have them backwards.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5237525 10/12/19 12:32 AM
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oldhp Offline
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Pretty sure the brake filament is brighter than the tail light filament, so it does make a difference. Hook a dedicated ground wire up thru your wiring connection that goes from the light bulbs/lightbulb sockets thur the connection to a known ground on the truck.


"None of us are getting out here alive.....drink that beer.....eat that pizza......drive that Hot Rod"
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Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5237713 10/12/19 10:26 AM
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JLTD Offline
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Why not just test them as installed and if they work properly, they work properly. Switch wires if they don't. You could also trace the wires back a bit to where they hadn't been painted.


Most bulbs don't care about which way the current is flowing.


I use the overseas manual to choose my viscosity.

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Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5237802 10/12/19 12:36 PM
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Other than the wires causing a direct short what makes you think damage would occur


2015 F150 2.7
2018 F350 6.2
Re: Any harm in hooking up trailer lights backwards? [Re: JLTD] #5238104 10/12/19 08:27 PM
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motor_oil_madman Offline OP
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Originally Posted by JLTD
Why not just test them as installed and if they work properly, they work properly. Switch wires if they don't. You could also trace the wires back a bit to where they hadn't been painted.


Most bulbs don't care about which way the current is flowing.


I don't think they were concerned with color coding when they built this trailer, otherwise I would have done that.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5238106 10/12/19 08:28 PM
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motor_oil_madman Offline OP
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It's only the passenger side that looks the same. Somehow the brown and green look the same.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5239206 10/14/19 09:56 AM
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mk378 Online Content
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Plug in the truck, turn the running lights on, then touch what you think is the brown trailer wire to each light wire. Use the one that lights up dim. If the "brown" wire seems dead, try the other one. By elimination, the other wire is the turn / brake.

Always run a network of ground wires (standard color is white) to each light and the truck plug. Do not count on grounding through the frame.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5239793 10/14/19 09:57 PM
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motor_oil_madman Offline OP
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Mk378 do I have this right? I have a ground wire on each tail light attached to clean shiny metal on the trailer and then one ground wire that.goes from the truck plug to the tongue of the trailer, also connected to clean shiney metal. It still seems to only be grounding through the ball though.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: Any harm in hooking up trailer lights backwards? [Re: motor_oil_madman] #5240084 10/15/19 10:23 AM
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mk378 Online Content
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Run a ground by wire all the way from the truck plug to each light. You don't need an individual wire for each light, you can tee them into a common wire. Don't involve the trailer frame at all.

It is also possible that the ground socket on the truck is not grounded to the truck. That would cause what you're experiencing. With the lights on, the ground wire in the trailer plug should be zero volts measured to the truck frame.

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