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Old 10-18-2019, 12:07 AM   #1
kipps
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Factory trailer brake controller and plug?

Were there any factory provisions in these 73-87 trucks for towing? Either a brake controller or a trailer plug? Were there "factory-approved" dealer hang-on options? Or was any form of trailer connection just left to the individual owner?

It seems strange that GM would have ignored the basic needs of towing, but I've never run across any evidence of such either.
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Old 10-18-2019, 12:35 AM   #2
kwmech
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Re: Factory trailer brake controller and plug?

I've never seen any factory stuff, always dealer add-on or aftermarket from the 'trailer place'.
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Old 10-18-2019, 07:02 AM   #3
Keith Seymore
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Re: Factory trailer brake controller and plug?

No - no factory provisions for squarebodies.

It's just where the industry was as a whole, at that time.

We didn't have a trailering engineer/expert until about halfway through the squarebody era.



K
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Old 10-18-2019, 07:09 AM   #4
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Re: Factory trailer brake controller and plug?

I integrate Pollak 7-round kits into my rear taillight harnesses as an option-not a fan of how “it used to be done” with add-on crimp splices, electrical tape...ugh!
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Old 10-18-2019, 07:52 AM   #5
Greenlee
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Re: Factory trailer brake controller and plug?

There are after market trailer harnesses that plug into the factory harness for the lights. I have one on my truck.
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Old 10-18-2019, 08:29 AM   #6
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Re: Factory trailer brake controller and plug?

Quote:
Originally Posted by Keith Seymore View Post
No - no factory provisions for squarebodies.

It's just where the industry was as a whole, at that time.

We didn't have a trailering engineer/expert until about halfway through the squarebody era.



K
When did GM start putting the un-terminated pair of trailer wires in the taillight harness?
I thought the camper special package had some kind of extra wiring.
Both of My T400 trucks 1995 & 2000 had trailer Brake and Breakaway Battery Charge wires bundled into the taillight wiring that I've never seen on a squarebody.
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1969 Dodge Polara 500 B383, A833 SOLD
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1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
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Old 10-18-2019, 09:04 AM   #7
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Re: Factory trailer brake controller and plug?

I am 99.9% sure GM never did. For one, the OE 4-way rubber vulcanized connectors are obsolete so nobody is going to offer a direct plug in for lights-even for a 4-way flat...and there is NO way they offered one for a 7-round since it requires a more substantial frame ground as well as a control wire and power +12V feed from the front, fused. So extremely doubtful they had a 4-flat ever and NEVER offered a plug in for 7-round trailers.
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Old 10-18-2019, 09:38 AM   #8
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Re: Factory trailer brake controller and plug?

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Originally Posted by gmachinz View Post
I am 99.9% sure GM never did. For one, the OE 4-way rubber vulcanized connectors are obsolete so nobody is going to offer a direct plug in for lights-even for a 4-way flat...and there is NO way they offered one for a 7-round since it requires a more substantial frame ground as well as a control wire and power +12V feed from the front, fused. So extremely doubtful they had a 4-flat ever and NEVER offered a plug in for 7-round trailers.
Curt and Hopkins made a Tee tap for the 1968-1982ish round rubber molded tail-lamp wiring plug to four way flat trailer plugs. You can still find em on eBay.
Curt 55311, Hopkins 39759TM

Tekonsha, Curt, and Hopkins still make em for the 1983ish-1991 square 2x2 four terminal Weatherpak tail lamp plug.
https://www.etrailer.com/t1-1985_Che...ies+Pickup.htm

The Tee connections are just for the four hot wires to the lights. You still need the ground connection to the frame. I usually use a ring terminal and star washer at the bumper-to-frame mount bolts for the trailer ground. You could drill a 1/4" hole and run a bolt and star washer through the frame at the new hole.
If you're just hooking up a 4way flat rubber trailer plug a ground wire sufficient for lighting only is in the included pigtail... it's done...

If your trailer has brakes you'll need to clip off the plug and run additional wires up to the cab to wire up a 7 blade jack. The brakes and breakaway battery draw a lot more current than the lights DON'T USE the ground wire from the four position rubber trailer plug with brakes.

If you have a trailer setup with the archaic round 6 or 7 position round plug with round pins just install the industry standard 7 blade jack on the truck and buy an adapter plug. My 7 blade jack has a 4 position flat plug connector as well. I carry adapters that go from 7 blade jack to the obsolete round plugs that I need. Both adapters also have flat plug connections.

The 12ga BLUE brake and 12ga RED breakaway battery will likely need to be run and without question the 12ga WHITE ground to the frame. I've found solid copper and THHN house wire run along frame rails by Bubba for these wires. Do it right with 12ga SXL wire.
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1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 10-18-2019 at 10:19 AM.
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Old 10-18-2019, 11:14 AM   #9
Keith Seymore
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Re: Factory trailer brake controller and plug?

I guess I should clarify:

We did have trailer lamp harnesses that coupled into the tail lamp harness using factory electrical connections. That started about halfway through the product lifecycle.

My mind immediately went to integrated trailer brake controllers: we never had any kind of connected provisions like they did for the GMT800 trucks and beyond. It's all splice and dice.

K
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Old 10-18-2019, 01:06 PM   #10
gmachinz
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Re: Factory trailer brake controller and plug?

Me as well...I was thinking of 7-round kits mainly.
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Old 10-18-2019, 02:57 PM   #11
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Re: Factory trailer brake controller and plug?

Quote:
Originally Posted by Keith Seymore View Post
I guess I should clarify:

We did have trailer lamp harnesses that coupled into the tail lamp harness using factory electrical connections. That started about halfway through the product lifecycle.

My mind immediately went to integrated trailer brake controllers: we never had any kind of connected provisions like they did for the GMT800 trucks and beyond. It's all splice and dice.

K
That level of integration really surprised me when I brought the T800 home.

Both of my T400 trucks just had coiled up un-terminated Blue and Orange?? wires with heatshrink over the ends. Not positive about that second color.

The Squares all had some kind of trailer wiring installed by Bubba or U-wreckit using Scotchlok taps. I've usually had to replace the green puss filled taillamp to cab wiring and sometimes the actual lamp wiring pigtail as well. I pull Blue and Red 12ga brake and battery wiring in with the four replacement taillamp wires regardless of whether the end product will have a hitch.
I have yet to see the factory trailer or camper light prep even tho the wiring books have a harness diagram for them. I've had several camper special trucks but none of them had the original wiring in the rear. I was wondering if they actually existed outside of the GM wiring books.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 10-18-2019 at 03:04 PM.
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Old 10-18-2019, 03:51 PM   #12
demian5
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Re: Factory trailer brake controller and plug?

My 73 C20 Suburban had one that Ive seen on a lot of trucks, its plumbed into the brake line at the master cylinder. It had a knob to actuate and a wood grain sticker. MH?
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Old 10-18-2019, 03:59 PM   #13
kipps
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Re: Factory trailer brake controller and plug?

Quote:
Originally Posted by demian5 View Post
My 73 C20 Suburban had one that Ive seen on a lot of trucks, its plumbed into the brake line at the master cylinder. It had a knob to actuate and a wood grain sticker. MH?
Most likely a Kelsey Hayes. Evidently a very common controller back in the day, and still arguably the best you'll find for an older truck. If you intend to tow, that one would be better than any newer ones you buy now.

http://67-72chevytrucks.com/vboard/s...d.php?t=782914
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Old 10-18-2019, 05:09 PM   #14
Keith Seymore
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Re: Factory trailer brake controller and plug?

Quote:
Originally Posted by hatzie View Post
That level of integration really surprised me when I brought the T800 home.
I loved those.

At that time I was driving company owned vehicles, so I could browse the fleet, pick whatever I wanted, and within a few minutes have my brake controller installed and ready to rock and roll.

Another enthusiast and I independently discovered a problem in that way. When the Global A electrical architecture was released for the 2003 model year they changed a couple pinouts and didn't tell anybody. The net result was no trailer brakes. I realized it while I was on the phone with the Electrical system engineer trying to figure out why I had no brakes; the other guy found out when he hit the end of his driveway.

They ended up releasing a new jumper harness, with a new part number and a color coded connector as a result. I still have a library of those harnesses in the cabinet.

K
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Old 10-19-2019, 11:38 AM   #15
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Re: Factory trailer brake controller and plug?

Quote:
Originally Posted by kipps View Post
Most likely a Kelsey Hayes. Evidently a very common controller back in the day, and still arguably the best you'll find for an older truck. If you intend to tow, that one would be better than any newer ones you buy now.

http://67-72chevytrucks.com/vboard/s...d.php?t=782914
Yeah my first job was installing those and hacking in trailer lights, at a travel trailer sales lot. I didn't even have my license yet but I was moving around up to 25' trailers on the lot with an ~1963 red Chevy long wide pickup (283 and 4 speed).

After I bought my 1973 brand new, I installed the brake controller up in the little pocket (no a/c) above the heater controls. It was a smaller controller though than the older flat style KH. I drilled a hole in the back of the dash pocket for the brake line and wires.

I'm pretty sure my 1991 Suburban has factory trailer light "tee" under the back (along with a factory receiver?). Seems like I just bought the adaptor to plug right in. I never messed with brakes because our 17' trailer is only about 2K pounds which isn't much behind a Suburban. Pickups carry campers that heavy and don't have an extra braking axle.
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