How do you wire a Macgregor trailer to a GMC Sierra Pick Up

[Gunkholer]

Hi All.

I bought a 26X and need to wire my truck to trailer. The trailer has a 4 pin black plastic connector on it. One pin looks like its prolly a ground but what are the other three? My truck has 5 wires technically.

1. Ground
2. Right Turn Signal
3. Left Turn Signal
4. Brake
5. Running Lights.

How do I hook 5 wires on the truck to 4 wires on the trailer.

Please help so I can go pick my new boat up tomorrow.

Thanks!

[K9Kampers]

You should be able to go to any auto parts store, including SprawlMart, and buy a towing harness for your specific vehicle. They are plug-&-play, to the vehicle's taillight connectors. No cutting, splicing, trial & error, cussing...

There are also all sorts of vehicle / trailer plug adapters - 4 pin to 5 pin, bullet to flat, etc... If the trailer has a 4 pin connector, then it won't (shouldn't) be wired for brakes, most likely surge brakes anyway

[Jim Bunnell]

My 2003 trailer has the flat 4 pin connector; a simple 4 flat to 5 round adaptor plugged into my Yukon (same basic vehicle as your truck) and all was well.

[atzserv]

i have an Escalade and it has an oval connection on the vehicle. I bought an oval to flat adapter that has both the 4 and 5 flat pin connections( 2 seperate flat connectors). I went to a travel trailer outlet and got it. If you need the 5 pin flat going into oval they are hard to find at walmart or even auto stores. I dont know which pin it is but the flat that has 5 pins is to provide power to the elec brakes. If all you need is a 4 pin going to the oval connector, they are everywhere. Same oval connector on my trailblazer so must be a GM standard as far as the oval factory connections go.

[Gunkholer]

Hey guys I got it figured out. I have 5 wires in my wire harness on my truck. (don't know if it is a "tow package" thing or not since I bought my truck used) I only have 4 wires on the trailer. The answer is a relay at the store that has 4 wires on one end and 5 wires on the other end. You just solder them to the plugs and harness and you're ready to go. About $12.99 for the converter. Problem solved.

Thanks guys!

[tangentair]

!	tangentair:
	Moved to a more appropriate forum

[Gunkholer]

Well guys the problem is not soleved I guess. There was a 4 wire to 5 wire connector that I thought worked but as it turns out it ran everything but the brakes. Running lights, turn signals, and hazards work great, just no brakes. Since the brakes I assume are the same basically as the turn signal I thought the little converter might have been burned out when I bought it new so I bought another one but this time heavier duty. Same problem, no brakes.

The brake wire works going into the converter but not coming out.

I'm stumped. Anyone got any ideas?

[Frank C]

That "brake wire" should be connected to the backup lights. It's intended to DISABLE the surge brakes when you're in reverse. IF you're saying the brakes are not working at all, then you have the wrong input wiring, permanently disabling the trailer brakes, rather than only during reverse gear.

[Gunkholer]

Sorry I meant brake "lights". The brakes work fine, its the brake lights I cannot get to work.

This is the wiring chart that came with the vehicle:

Brown = Parking Lamps
Light Green = Back Up
Dark Green = Right Turn
Yellow = Left Turn
White = Ground
Blue - CHMSL (center hight mounted stop light)


I've used the blue as the brake light. Maybe thats my problem?

[Hamin' X]

What model year is your pickup?

~Rich

[Gunkholer]

2000 GMC Sierra

[Hamin' X]

The 2000 GMC has separate turn and brake lights, while the trailer uses the same bulb for both. You are on the right track with the converter plug. If your pickup does not have the tow package, then someone has wired the trailer plug receptacle themselves and all bets are off as far as color codes go. You should not use the center high mounted stop light line, no matter what color it turns out to be. This is a low amperage circuit and will not carry the load of incandescent bulbs. To check to see if you have the factory tow package wiring, look under the hood on the port side of the engine compartment. There is a black plastic covered box. Remove the lid and check for fuses in there that are labeled for the trailer, or Trl. Stop, turn, tail,etc. If the slots are empty and have no terminals in them, then you do not have the tow package.

If by checking with a meter, or test light on your existing wiring, you have verified that you have left turn, right turn and taillights. This is all that you need, do not use a separate brake wire. The converter will combine the turn signal lights to work together for brake lights and split them when both a turn indication and brake lights are needed.

Lots of good info at eTrailer with wiring info and trouble shooting guide Here.

Good luck ~Rich

[Gunkholer]

Excellent information! Thanks Rich. I just ran out & checked and my truck does have all the trailer fuses in the fuse block. So I’ll clip the brake wire from the converter and see if this does the trick.

Thanks again!

[Frank C]

The 2000 GMC has separate turn and brake lights, while the trailer uses the same bulb for both. You are on the right track with the converter plug. If your pickup does not have the tow package, then someone has . . .
Good luck ~Rich

WHOA~!!
What an amazingly informative & useful post ... you 'da MAN, Rich!

[Gunkholer]

Man o man I am having the worst luck with this! My truck has separate lights for brake and signals, and my trailer has the same bulb for the brake and signals. I cannot figure out how to get the two to talk to each other. I've tried three different converters and wiring every which way but loose and I still cannot get them to work while pressing down the brake.

I guess the only thing left to do is add another light to the trailer and use that light exclusively as the brake lights only.

Thanks for all your help guys! I appreciate everyone's suggestions.

Guess there's still some things in this world that are unsolvable.....