Factory trailer brake controller and plug?

[kipps]

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.

[kwmech]

I've never seen any factory stuff, always dealer add-on or aftermarket from the 'trailer place'.

[Keith Seymore]

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

[gmachinz]

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!

[Greenlee]

There are after market trailer harnesses that plug into the factory harness for the lights. I have one on my truck.

[hatzie]

Originally Posted by Keith Seymore

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.

[gmachinz]

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.

[hatzie]

Originally Posted by gmachinz

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.

[Keith Seymore]

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

[gmachinz]

Me as well...I was thinking of 7-round kits mainly.

[hatzie]

Originally Posted by Keith Seymore

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.

[demian5]

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?

[kipps]

Originally Posted by demian5

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

[Keith Seymore]

Originally Posted by hatzie

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

[1976gmc20]

Originally Posted by kipps

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.