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Old 06-02-2020, 09:32 PM   #1
thedudeabides86
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What do you all use for trailer light hookups?

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!
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Old 06-02-2020, 09:51 PM   #2
Mike C
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Re: What do you all use for trailer light hookups?

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.
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Old 06-02-2020, 10:25 PM   #3
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Re: What do you all use for trailer light hookups?

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Originally Posted by Mike C View Post
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
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Old 06-02-2020, 10:51 PM   #4
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Re: What do you all use for trailer light hookups?

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

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Old 06-02-2020, 11:11 PM   #5
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Re: What do you all use for trailer light hookups?

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.
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Old 06-03-2020, 07:48 AM   #6
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Re: What do you all use for trailer light hookups?

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.
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Old 06-03-2020, 01:05 PM   #7
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Re: What do you all use for trailer light hookups?

I have to agree, that's a little bit of mess under there.. the harness wrapped in a sleeve leading thru the bumper ends in a receptacle of some type? 6 pin as Mike suggests it might be, was a common connector.. could also be 4 or 5 pin as well, depends on what it was previously wired up for..

that may be salvageable if it's already connected properly and you can find an adapter.. or just to get down the road, peel back the tape and splice in but that should be temp only for an urgent tow..

personally, I would do what Mike suggests and start over.. that could all be cleaned up as he suggested to a factory style for lights only, basically boat trailers..

if you intend to use this truck for other future towing needs, I would install a modern standard 7 round RV style and use whatever adapters you need from there.. especially if there is already a receptacle hole in the bumper.. 7 flat or RV style is the most common connection you'll encounter today and fairly hardy.. if you don't want the modern appearance of the 7 pin connector, tuck it up under there so it's out of sight during normal driving without a tow..

this site has about the most comprehensive trailer wiring information out there..

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

7-Way Connectors
Aside from the three main lighting functions, additional pins for electric brakes, a 12 volt "hot" lead, and backup lights are available. There are two types of 7-way connectors. One has flat pins, which are often referred to as blades. The other has round pins. The round pin style is very rare. The RV style 7-way with flat pins (or blades) is very common. It is often found on newer trucks and SUVs that come equipped from the factory with a trailer hitch.

one thing that always bothered me with swapping trailers among friends, rentals, etc. was the occasional wiring confusion.. "oh my trailer is right, your truck is wrong" BS.. drives me nuts!

I suggest you do yourself a favor and follow the standard for whichever connector you choose.. as you acquire more trailers and tow vehicles, keep following the standard and you'll have much less trouble.. and whether you save what's there or start over completely from factory connections, I would also suggest investing a some premium electrical connectors with solder and heat shrink to provide corrosion free connections for a lifetime..

good luck!
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Old 06-03-2020, 01:16 PM   #8
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Re: What do you all use for trailer light hookups?

Agree with the above. Back in the day the 6-round was common. I had that on my trailer and carried a home made 6-round to 4-flat adapter for pulling those. Now I have a 7-round on the truck and carry 1 adapter for 4 and 6 flat and another for 6-round. I too would do a new tail harness, those splices will eventually fail-and at the most inopportune time.
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Old 06-03-2020, 07:44 PM   #9
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Re: What do you all use for trailer light hookups?

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.
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Old 06-03-2020, 08:46 PM   #10
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Re: What do you all use for trailer light hookups?

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 .
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Old 06-03-2020, 09:21 PM   #11
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Re: What do you all use for trailer light hookups?

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.
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Old 06-04-2020, 07:46 AM   #12
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Wink Re: What do you all use for trailer light hookups?

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
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 06-09-2020, 09:39 PM   #13
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Re: What do you all use for trailer light hookups?

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?
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Old 06-09-2020, 09:52 PM   #14
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Re: What do you all use for trailer light hookups?

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!!
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Old 06-09-2020, 10:07 PM   #15
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Re: What do you all use for trailer light hookups?

Quote:
Originally Posted by 53burb View Post
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.
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Old 06-09-2020, 10:39 PM   #16
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Re: What do you all use for trailer light hookups?

Quote:
Originally Posted by 53burb View Post
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.
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Old 06-09-2020, 10:51 PM   #17
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Thumbs up Re: What do you all use for trailer light hookups?

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
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 06-09-2020, 11:27 PM   #18
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Re: What do you all use for trailer light hookups?

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

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Old 06-09-2020, 11:54 PM   #19
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Re: What do you all use for trailer light hookups?

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
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Old 06-09-2020, 11:55 PM   #20
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Re: What do you all use for trailer light hookups?

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


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Old 06-10-2020, 02:01 AM   #21
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Re: What do you all use for trailer light hookups?

I am going to use one of these hopkins 4 and 7 pin outlet
No adapers tow pretty much most trailers
#HPK1200409055

I am using American autowire factory replacement harness to replace intermediate and taillight harness
No messing around with 48 plus year old wiring no mess no fixing previously hacked wire

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Old 06-11-2020, 01:36 AM   #22
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Re: What do you all use for trailer light hookups?

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.
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Old 06-13-2020, 12:46 AM   #23
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Re: What do you all use for trailer light hookups?

Quote:
Originally Posted by Killer Bee View Post
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


So, update. I picked up the plastic bodied adapter and tested it. I had brakes and emergency flashers but no left turn or right turn signals. I’m not sure how to correct that issue. Any suggestions?
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Old 06-13-2020, 10:13 PM   #24
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Re: What do you all use for trailer light hookups?

Quote:
Originally Posted by thedudeabides86 View Post
So, update. I picked up the plastic bodied adapter and tested it. I had brakes and emergency flashers but no left turn or right turn signals. I’m not sure how to correct that issue. Any suggestions?
just found half of a gibberish reply I never finished last night in my cell phone, not that this one will be much better

follow the schematic with a test light, meters usually don't respond fast enough, and find out where the circuit is open for those functions..

maybe the wire harness under the truck to the back of the receptacle, new adapter could be bad, trailer connector, etc..

maybe bad connections or incorrect wiring, check both ends to make sure they're connected correctly..

2 down, 2 to go - good luck!
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