Trailer wiring harness

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Lord Les
Regular Member
Posts: 79
Joined: Mon Aug 15, 2011 8:09 pm

Trailer wiring harness

Postby Lord Les » Wed May 16, 2018 9:39 pm

I'm putting in a wiring harness for a trailer. Used some oven cleaner to clean the wires for my photo. I'm using a four wire harness, and I'm wondering which wire is for what. I mean, on the truck, not the harness. Sorry if this is stickied somewhere. Hope you like my photo.

Looks to me like red, black, green with black stripe and green with red stripe, and solid green, and probably another one. :P
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1983 diesel Pup w/ long bed and manual transmission (no AC) and ugly ugly paint

oldestisuzuist
Regular Member
Posts: 1286
Joined: Tue Oct 07, 2008 9:10 pm
Location: N W Arkansas

Re: Trailer wiring harness

Postby oldestisuzuist » Wed May 16, 2018 11:12 pm

I would buy a tester with a sharp probe that penetrates the wire insulation & indicates when power is present. Test each wire to see what it powers.
You'll also need a converter, something like a Hopkins #46155 or #48915 or #1143285 if you have the big connector for plug & go. These convert the separate turn & brake lights to a standard 4-flat with ground connector for the trailer lights to plug into.
If you can't find anything specifically for an Isuzu one for a Toyota pickup will work using individual wire splices
'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, body ROUGH, bought new 12/4/78. A pre-P'up?
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch.

Lord Les
Regular Member
Posts: 79
Joined: Mon Aug 15, 2011 8:09 pm

Re: Trailer wiring harness

Postby Lord Les » Sun May 20, 2018 5:30 pm

I borrowed an induction tester, but even though the turn signal is on, it isn't detecting anything. I bought a wire harness from Harbor Freight for 8 bucks. It has the trailer and vehicle wires with the 4 flat connector. And it has quick connect splice which is as simple as it gets.

I have the original big connector that connects the tailights etc with the front of the vehicle. Is there something that just lets me connect in between the plug? Someone said something about a Toyota in another thread but then never explained which wires need to be moved.

I have someone hopefully coming tomorrow to do some steering work on an old Aerostar and if I don't get it soon, I'm just going to ask them to do it.

It's too bad that there isn't a simple wire identifier page. I'm assuming I have factory wiring.
1983 diesel Pup w/ long bed and manual transmission (no AC) and ugly ugly paint

oldestisuzuist
Regular Member
Posts: 1286
Joined: Tue Oct 07, 2008 9:10 pm
Location: N W Arkansas

Re: Trailer wiring harness

Postby oldestisuzuist » Sun May 20, 2018 8:15 pm

If your truck has this type connectors https://www.ebay.com/itm/CURT-55305-Cus ... 7P&vxp=mtr you simply plug the trailer wiring connectors into the appropriate truck connectors, no wire splicing or identifying required. if your truck has different connectors then you will have to indentify each wire function & splice the appropriate wires together through a converter
The $8 Harbor Freight 4-wire trailer wiring kit won't work, it won't hook up the individual signal lights, which require either a converter or 5 wires. Something like this https://www.ebay.com/itm/NEW-Hopkins-To ... 9L&vxp=mtr even has a tester, will require identifying each wire, then quick-splicing to the correct wire in the wiring harness.
You can quick-splice something like this https://www.ebay.com/itm/48915-Hopkins- ... I5&vxp=mtr for a little cheaper, then use the trailer portion of the Harbor Freight harness to connect directly to the converter.
'78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, body ROUGH, bought new 12/4/78. A pre-P'up?
'87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch.


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