Wire in a 7 pin trailer hookup from scratch

[jhiggy94]

Hi guys,
Im a total noob when it comes to wiring but right now i am wiring up my 72 Chevy k20 with a kit that i bought. So im learning a lot but i still have no idea how to install any kind of trailer pin. So i want to install a 7 pin trailer hookup. There is nothing installed right now not even a 4 pin and i am completely unsure of where i have to start. Is there any kits that would help me? Do i have to run 7 new wires from somewhere up front? Any help would really be appreciated. Thanks guys

[Gonepostal]

Try this http://www.chuckschevytruckpages.com/trailerlights.html

[JJorgensen52]

http://www.etrailer.com/faq-wiring.aspx

This is by far the best wiring FAQ I've found for this subject.

You'll have to run a couple of wires from up front. On the rear cross-member the factory rear light harness contains the following wires (on our trucks they match standard trailer colors, I found it easiest to trace them from the lights):
-Left Turn
-Right Turn
-Stop
-Park/Tail/Marker.

You can tap into those using wire taps, or I believe there is a splitter available which goes in where the rear harness joint is near the rear axle, which can be modified to suit this purpose.

The remaining 3 wires are:
-12v+ feed (20A fused, recommended to use a self resetting breaker)
-Ground (you can go to the chassis at the rear, or run up front, any good clean ground will work)
-Brakes - this is the power feed wire (the standard color is blue, should be 10ga) which would come from your brake controller in the cab. This is also fused with a self resetting breaker, rating 20A - 30A depending on your setup.

Walmart sells a 7-way connector kit made by Hopkins which includes all the wiring you need. Brake controller kits often come with wiring, as well.

[FirstOwner69]

Below is a link to a to a plug-in wiring harness connector by Hopkins that should eliminate the splicing you'd need to do for the 4 basic wires (right turn, left turn, tail/marker lights and ground... if the ground is part of the truck harness). As a clarification, there is no separate stop wire. Then you'd need to add 12v hot and trailer brake wires as described by JJorgensen52. You may also want to splice into the truck backup light wire if you have backup lights on your trailer. That takes care of all 7 wires.
http://www.hopkinstowingsolutions.co...ban_73-84.html

[MARKDTN]

Originally Posted by FirstOwner69

Below is a link to a to a plug-in wiring harness connector by Hopkins that should eliminate the splicing you'd need to do for the 4 basic wires (right turn, left turn, tail/marker lights and ground... if the ground is part of the truck harness). As a clarification, there is no separate stop wire. Then you'd need to add 12v hot and trailer brake wires as described by JJorgensen52. You may also want to splice into the truck backup light wire if you have backup lights on your trailer. That takes care of all 7 wires.
http://www.hopkinstowingsolutions.co...ban_73-84.html

Something like this is the best solution. As someone who is in the body builder industry, you want to splice as little as possible-especially outside the vehicle. Use connectors that "Y" the factory as much as you can. With all the nasty road chemicals in use today in winter, it does not take much to ruin a harness.

[jhiggy94]

Originally Posted by FirstOwner69

Below is a link to a to a plug-in wiring harness connector by Hopkins that should eliminate the splicing you'd need to do for the 4 basic wires (right turn, left turn, tail/marker lights and ground... if the ground is part of the truck harness). As a clarification, there is no separate stop wire. Then you'd need to add 12v hot and trailer brake wires as described by JJorgensen52. You may also want to splice into the truck backup light wire if you have backup lights on your trailer. That takes care of all 7 wires.
http://www.hopkinstowingsolutions.co...ban_73-84.html

So what exactly does this kit do? does it plug inline with the rear lights and gives a 4 pin trailer plug off of that? And then is there a way to modify that 4 pin into a 7 pin?

[capev86]

yeah, the adapter plugs right in between two existing plug ends just like on a modern vehicle. i picked one up years ago for my 72 Suburban and THEN found out that only the pickup and blazer can use it...the burb tail light harness is different and they routed the wires through the ceiling above the left side windows instead of underneath (only the license plate wire goes outside). better protected, but harder to add the trailer wiring.

[FirstOwner69]

Originally Posted by jhiggy94

So what exactly does this kit do? does it plug inline with the rear lights and gives a 4 pin trailer plug off of that? And then is there a way to modify that 4 pin into a 7 pin?

Yes to your first two questions.

To get the 7 pin setup, cut off the trailer end 4 pin plug. Then, buy a 7 pin connector (http://www.hopkinstowingsolutions.co...d_plastic.html) for the truck and wire these 4 wires and the additional 3 mentioned in the posts above into the 7 pin connector as shown in the links JJorgensen52 provided above. The Hopkins links I've given also provide links to PDF instructions.

This will minimize the number of splices giving better connections, reduce the potential for environmental contamination and give a much cleaner installation.

[capev86]

you could cut off the 4 prong plug and wire it in, but i would suggest gettting a plug in 4 to 7 conversion also so all you have to do wire up the two circuits for the brakes, and the wire for the trailer battery charger.

[Davemotohead]

I just made another wiring harness and ran it along with the stock one to the rear from the engine compartment,,I ran about 10 wires of different sizes (Good to have extra's) I used the B/U light terminal for flood lights on my trailer operated from a switch on the dash,also have floods under the bumper of the truck and run a power inverter to get 110 A/C to run stuff,,maybe over kill but I have extra wires left if I want to add anything else

[jhiggy94]

Thanks a lot for all the info. This has been a big help

[eagleuh1]

If you're wiring for an older Airstream, they're different positions in the plug. I found that out the hard way when I bought my trailer and towed it home.
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[capev86]

what you do is wire up the truck with the circuits in the standard position. then you make a shorty adapter for the trailer. that way you can hook up to any trailer.

on our 71 Holiday Trav'ler, my Dad made an adapter for the shore power plug in because hookups at some campgrounds can be backwards.

[JellyBeanDriver]

You might want to get an isolator down the road. Especially for the parking lights, adding more load to the already thin gauge factory wiring can cause problems like overheating at the light switch connector.

Just went through this on an 86' C30. Replaced a bunch of burned wiring from a trailer short. Got much of what I needed from donor vehicles at the junkyard and a lot of those showed overheated parking light wiring at the light switch connector for those trucks that had trailer hookups. Many also had larger fuses installed in the fuse boxes and the wiring at the fuse box showed overheating damage.