Correct way to wire in trailer plug

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Correct way to wire in trailer plug

Postby matthewh » Fri Jul 25, 2014 2:04 pm

As stated, what's the best solution to wiring in a trailer plug at the back of the truck? I've seen the adaptor kits from Curt, Reese, etc that plugs behind the taillights and gives you a 4 way flat, however, I've read elsewhere that doing so is a disaster waiting to happen, believe it was on TDR, mystery man mentioned using relays and such, basically a whole separate harness to achieve this.

The dually already has a 7-way RV plug in the bed, for the 5th wheel hitch that's no longer there, and id like to keep that there, but add another 7-way and a military plug out at the bumper to accommodate bumper pull trailers.

If possible, id like to remove the current wiring, patching and fixing the spliced factory harness, and run a separate harness for the towing plugs, but I've got no idea a schematic to do so. Has anybody done this, using relays and such, or am I over thinking this

Thanks
'93 W350 5spd Getrag, 4.10 gears, 83k miles and counting, Mods: LPPP AKA Ma Dually
'54 Dodge M37 6.2/700R4/205, 5.89 gears, WC rear axle
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Re: Correct way to wire in trailer plug

Postby cmann250 » Fri Jul 25, 2014 3:52 pm

Use these: http://www.etrailer.com/t1-1989_Dodge_R ... nd+Chassis

No factory harness cutting necessary. Snip off that useless 4 prong end and use eyes to wire in the 7 blade plug. The T harnesses I have (likely 20+ years old) have the running lights coming off of one harness and the back up lights coming off of the other. I guess back up lights aren't common any more.

On the military plug, I'd just make my own harness the right way, i.e. loom, shrink tubing, etc.

Relays wouldn't be a bad idea, but in my opinion they aren't necessary unless you are pulling a 40' enclosed gooseneck with incandescent running lights every 12", top and bottom. Who knows how long those T harnesses have been under my truck and they don't show any corrosion now.
Caleb, Certified Shade Tree Mechanic Extraordinaire :mrgreen:
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Re: Correct way to wire in trailer plug

Postby oldestof11 » Fri Jul 25, 2014 3:57 pm

Jon
93 D250~ Mismatch of cheap parts, trying to look fast going slow
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Re: Correct way to wire in trailer plug

Postby PToombs » Fri Jul 25, 2014 5:29 pm

I would use the T tap trailer harness set up and wiring the tail light circuit on a relay is a good idea. Any load you take off the light switch will increase the longevity of the switch.
pete

Just enough power to break everything behind the crankshaft.
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Re: Correct way to wire in trailer plug

Postby DodgeFreak » Fri Jul 25, 2014 5:32 pm

I wouldn't worry about running relays......we run 7 pin round tied into the factory harness on several of our trucks with no problems....Like Caleb said, unless you run a ton of trailer lights I wouldn't worry about it...
92 D350 Cab and Chassis. Auto stock, wiring gremlins. 330k miles
92 W250 Ext cab rotted completely out. Auto, pump maxed, 215 ppump nozzles, Denny T2 pin.
85 D350 single wheel, converted to cummins, getrag, turned up 2 turns and afc screw flush.
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Re: Correct way to wire in trailer plug

Postby matthewh » Fri Jul 25, 2014 5:36 pm

I already have the headlights on a relay, jim lane method. My original idea was the t tap, and modify it to accept the 7-way and the military plug, that way any chance of corrosion is in the replaceable harness.

Being id like some reverse lights too, that crown Vic power box may not be a bad idea. I'll have to read up on that and see everything involved
'93 W350 5spd Getrag, 4.10 gears, 83k miles and counting, Mods: LPPP AKA Ma Dually
'54 Dodge M37 6.2/700R4/205, 5.89 gears, WC rear axle
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