What do you all use for trailer light hookups?

[thedudeabides86]

Hi.

My father in law has a sweet sea green 73 Starcraft fishing boat that he got from his father in law. We're working on getting it ready to go to the lake after ten years and it would look sweet behind the ol truck. What kind of wiring harness was factory back in 1972 on the C20's? The trailer has a flat 4 way harness and it looks like the underside of my truck has a round sort of plug on it. I haven't dug deep into it yet, as I thought I'd check with the fine folks of 67-72 chevy trucks. I appreciate the feedback and advice. Thanks!

[Mike C]

you can buy a "T" harness that plugs in between the taillight harness and the fusebox right by where spare tire mounts that has plug in wiring for trailer. Cost about $20.

[thedudeabides86]

Originally Posted by Mike C

you can buy a "T" harness that plugs in between the taillight harness and the fusebox right by where spare tire mounts that has plug in wiring for trailer. Cost about $20.

I'm snapping a few photos now. I also found this other thread. Thoughts?

http://67-72chevytrucks.com/vboard/s...d.php?t=288696

[Killer Bee]

if you have a standard 7 pin RV receptacle, you can buy a simple adapter..

I have one in my console for my boat trailer, plug-n-play, no wiring required..

good luck!

Napa Part #: BK 7551560 Trailer Wiring, Seven Way Round To Four Pole Flat Adapter

[thedudeabides86]

So, laying under the truck here's what I see. I'm assuming the two plugs hanging down are my trailer lighting. I'm not sure what the spliced wires are for...... aaaand of course the pictures posted all upside down. Ugh.

[Mike C]

Wow, that's ugly. I would consider a replacement tail light harness and the previously mentioned plug in adapter. It's expensive, relative to just plugging something in, but right way to clean that up.

The tail light harness plugs into the rear light fuse box harness on one of teh rear crossmembers about 2 ft from back of the truck. So you can throw all of that wiring away, attach the trailer light adapter and plug in the new tail light harness and that mess all goes away.

Eventually all that old wiring and splicing will give you troubles. But my guess is that plug that goes through the bumper is for a 6 pin trailer plug.

[burnin oil]

Hoppy makes a 7 pin RV plug with the the 4 blade boat trailer plug molded right next to it. Best of both worlds. Eliminates looking for the adapter. Trust me you always loose it when you need it. I spend an hour looking today for mine. I did find 3 separate hitch balls and slides in the process. Go figure none of them were the 2" I was looking for either.

[firedemon]

that's a start over harness . anything you are able to salvage from that is doomed to fail both for your trailer and your truck . I will say that seems to be the way it was done back in the day as it seems every time someone has asked me to check their lights it looks like that . if you can find them there are t connectors so you dont have to cut the wire harness and that would be the best way to go . if you decide to splice in to any wires outside the cab use marine grade shrink tubing it has a glue that will "help" seal the splice so water and road salt and other crap dont corrode the wires and give you problems . that being said I personally like the 7 pin with the 4 on the side and keep a couple adapters in the glove box just in case I tow something im not expecting . with the 7 pin you will have more wiring to do because it needs a trailer brake controller and a live power wire in addition to the lights .

[Rick Bollinger]

https://www.ebay.com/itm/rear-body-t...YAAOSwYS9ZYaK1

https://www.ebay.com/itm/rear-body-i...YAAOSwGBtZYZyH

https://www.ebay.com/itm/For-1968-19...ff2bb23dd7f676

Here are 3 Items that will clean up any issues from the firewall back. Its all just plug and play.

[Andy4639]

I would try this. Not sure about your year truck but it does fit my 71 truck for sure. I have it installed.

https://www.etrailer.com/Custom-Fit-...hoC8DgQAvD_BwE

[thedudeabides86]

Hey everybody. Sorry for the delay in responding. It's been a busy few days. I appreciate all the advice I've gotten. It's really helped. I was walking behind the truck a realized the cord under the bumper led to this spring loaded cover. It's a four prong, but I'm not savvy enough to know how to test it. Any suggestions?

[53burb]

get a 12v test light....ground the alligator clip, touch the tip to each one of the prongs:
1: push brakes, test light should be solidly lit
2: left blinker, test light will blink
3: right blinker, test light will blink.
4: one of the prongs is a ground...

That's not the typical 4-prong trailer hookup tho….best bet is to convert to the 4-pin flat style...that's the most common nowadays....

https://www.amazon.com/JASTIND-Autom...1754140&sr=8-2

there are cheaper ones....either way...ain't expensive & you will use it a lot!!

[thedudeabides86]

Originally Posted by 53burb

get a 12v test light....ground the alligator clip, touch the tip to each one of the prongs:
1: push brakes, test light should be solidly lit
2: left blinker, test light will blink
3: right blinker, test light will blink.
4: one of the prongs is a ground...

That's not the typical 4-prong trailer hookup tho….best bet is to convert to the 4-pin flat style...that's the most common nowadays....

https://www.amazon.com/JASTIND-Autom...1754140&sr=8-2

there are cheaper ones....either way...ain't expensive & you will use it a lot!!

Thanks for the input. I bought a wiring kit for my father-in-law's boat trailer ans with it came a 4 pin flat connector to connect to the vehicle. I figured I'd use that on the truck. I'm just not sure what wires to snip and solder it to. If you can make sense of the mess of wires in the photos I posted, you're an expert. I'll have to climb back under there are see what I can figure out.

[zosoppp]

Originally Posted by 53burb

get a 12v test light....ground the alligator clip, touch the tip to each one of the prongs:
1: push brakes, test light should be solidly lit
2: left blinker, test light will blink
3: right blinker, test light will blink.
4: one of the prongs is a ground...

That's not the typical 4-prong trailer hookup tho….best bet is to convert to the 4-pin flat style...that's the most common nowadays....

https://www.amazon.com/JASTIND-Autom...1754140&sr=8-2

there are cheaper ones....either way...ain't expensive & you will use it a lot!!

The left and right blinker pins are the brake lights. The other pins will be the non-brake (low) tail lights pin and a ground pin.

[Andy4639]

Here is the schematic for you with correct wires for the back of the truck.
Brown wire should be park lights & tag.
yellow for drivers side brake & turn signal.
Dark green for passenger side brake & turn signal.
Light green is back up lights.


https://farm4.static.flickr.com/3571...59575fe1_o.jpg

[Killer Bee]

apparently etrailer.com site is down right now, but the link I posted above has simplified wiring diagrams of them all.. worth checking back at a later time and keeping for reference

here's the 4 pin round, likely what you have there now.. looks their images are working still..



I would verify it's pinned correctly and just use an adapter like one of these for now.. fast, cheap, simple, and keep a functioning vintage connector..

clean up, rewire, add modern connectors, etc. as required or when you have time.. I am a huge advocate of solder/heat shrink sealed connectors and my favorite line "friends don't let friends use scotchlocks!"

plastic body $4

CURT 57224 Towing Electrical Adapter, 4-Way Round Vehicle Side to 4-Way Flat Trailer Side



metal body $8

CURT 57444 Towing Electrical Adapter, 4-Way Round Vehicle Side to 4-Way Flat Trailer Side

[dmjlambert]

You got this. Ask more questions if you need to. I take longer to type than other folks that have already replied, but thought I would go ahead and reply anyway, in case you want more detail.

1. disconnect the negative post of the battery
2. cut the 4 wires that go to the 4 prong connector that has the spring loaded cover.
3. track down which of those 4 wires goes to a screw or bolt and provides a ground connection.
4. strip the ends of the the other 3 wires and make sure the ends are not touching together or touching other things.
5. reconnect the battery
6. follow the instructions 53burb gave above using a test light to see which wire is for which purpose. Label them if you find them to be colors that don't match the purpose of each wire.
7. disconnect the negative terminal of the battery again.
8. connect your new flat 4 connector to those wire ends. If you want to get fancy you can remove the old 4 prong connector that has the spring loaded cover, put a grommet in the hole, and run the wires of your new flat 4 connector through the hole.
9. connect the battery and test the setup with trailer attached.

Here is a diagram of the wire colors and functions of the wires

[FirstOwner69]

Plug and play. Just unplug the taillight harness (if it's still there) and plug this in. The link also contains links to instructions and wiring codes.

http://www.hopkinstowingsolutions.co...fic/41105.html

[53burb]

thx for the correction!!


The left and right blinker pins are the brake lights. The other pins will be the non-brake (low) tail lights pin and a ground pin.