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

[Hamin' X]

Don't do anything rash, yet. I will try to check my set up and tell you how it works. I have a 2001 Chev Silverado and it has the same light set up as your GMC. All of my trailers are same bulb for both like yours. I do not have to use a converter. I think the truck does it for you. Wife is coming into town tomorrow and leaving Sunday morning, so it may be later Sunday before I can check out.

~Rich

[Gunkholer]

Ok Thank you.

I spoke with a buddy late last night and he will check his truck Sunday when he returns from his trip. He seemed to think the bumper plug was wired to the harness, but there was a round adapter from Chevrolet that plugged into that, which did the electronic switching.

I'll post after the weekend what I find.

Thanks again.

[Hamin' X]

As I said in my last post, I have a 2001 Chev Silverado. It has the factory towing package with a factory seven pin socket on the left side of the receiver hitch. The cover has a GM logo and the wiring diagram embossed on it. Wiring is as follows for the factory set-up:

Looking toward the socket and going clockwise:

• 1. At 1:30 + Positive

• 2. 3:00 Right Turn/Stop Light

• 3. 4:30 Electric Brakes

• 4. 7:30 - Negative

• 5. 9:00 Left Turn/Stop Light

• 6. 10:30 Tail/Running Lights

• 7. Center Pin: Backup Lights

Testing with meter indicates the following:

• With key on, when left turn is flashing, pin 5. is showing power on/off in time with the left rear turn signal on truck. Pin 2. is showing no power

• With key on, when right turn is flashing pin 2. is showing power on/off in time with the right rear turn signal on truck. Pin 5. is showing no power

• With key on, or off and brakes applied, Pins 2. & 5. are showing steady power.

• With key on and left turn flashing while brakes are applied, Pin 2. is showing steady power and Pin 5. is showing power on/off in time with the left rear turn signal on truck.

• Reverse Pin #s for right turn.

• Hazard lights flashing, both Pin 2. & 5. power on/off with the Hazard lights and show no brake light power when brakes are applied.

This all indicates that the conversion from separate turn and stop lights on the vehicle to same turn and stop lights on the trailer, is done on the vehicle, with no need for converter plug.

According to my owners manual, All GM pickups came with one of two wiring harnesses. A six wire Basic Trailer Wiring Package, or an eight wire Heavy-Duty Trailer Wiring Package. Wiring colors as follow:

For the Six wire:

• Yellow: Left turn/Stop

• Dark Green: Right Turn/Stop

• Brown: Tail/Running

• White: Ground

• Light Green: Back-up Lamps

• Light Blue: Center High-Mounted Stoplamp (CHMSL)

For the Eight wire package:

• Yellow: Left turn/Stop

• Dark Green: Right Turn/Stop

• Brown: Tail/Running

• White: Ground

• Light Green: Back-up Lamps

• Light Blue: Center High-Mounted Stoplamp (CHMSL)

• Red: Battery Feed

• Dark Blue: Trailer Brakes (Requires electric brake actuator)

If you do not have the factory trailer socket with the GM logo, someone has wired it themselves. You will have to go to the wiring harness at the frame to get the proper wire colors. The wires that you need for a four wire trailer are:

• Yellow: Left turn/Stop

• Dark Green: Right Turn/Stop

• Brown: Tail/Running

• White: Ground

This will give you all lights that you need for the trailer. If you want to use the electric deactivator for the surge brakes, use the Light Green Back-up wire for that. Do not use the other wires for any purpose on a boat trailer.

Hope this helps. ~Rich

[Gunkholer]

Hi Rich.

You must have the Heavy-Duty with the 8-wire package?

I do have the 6-wire setup. Like I said before, no plug, just bare wires. No OEM adapter to speak of neither......

When I test my yellow and dark green wires I do receive the turn signal voltage, but no power when the brakes are depressed.

I checked the fuses and they all look fine.

Do you think there is supposed to be some sort of OEM adapter to make the yellow and dark green wires show voltage when braking?

I just don't know what I'm missing here?

Ps. Thank you for taking the time to check your plug for me!

[Gunkholer]

Ok Rich I got it.

Thought about it for a while and was thinking there should be no difference between your truck and mine.

Pulled the fuses, filed terminals with a flat needle file and replaced with new fuses and viola!

We have brake lights now!

Thanks for your help in getting this figured out.

[Hamin' X]

Sorry that I missed your previous post and failed to answer. Glad that you figured out the problem and my pleasure to be of some assistance.

Just as a note to anyone else having electrical trouble: A fuse does not have to "look" bad to be bad. Sometimes fuses fail mechanically and the point of failure is not visible to the naked eye. Fuses are cheap. When in doubt, throw them out. Also in my personal experience, most strange things going on with electrical systems can be traced back to ground problems. By strange, I mean doing unusual things and/or having unexpected interactions with other systems. Again, these bad grounds may not be visible. Clean up those ground connections.

~Rich

[Scott]

Something to keep in mind in this post, some brake harnesses dont push enough juice to power anything besides the lights on the vehicle itself. On "The Beast" I had to install an auxiliary power box under the rear bumper to get the brake and turn lights to work on my Mac trailer.

This is the unit I have



Some Copy paste stuff

Why Is This Important?
In many cases the tail, turn and stop light circuits of today's vehicles are connected with light gauge wire, designed only to carry enough current to supply the lights the vehicle is equipped with. Additionally, some vehicles are equipped with sensitive electronic devices, such as "lamp-out" sensors, which are designed to monitor the vehicle's electrical system and warn the driver of problems with that system.

The additional load of trailer lights on these devices can cause them to react falsely and in some cases may lead to their failure.

Which Vehicles Need A ModuLite?

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Is the vehicle equipped with any option packages that include a lamp-out sensor or other electronic devices that could be damaged by attaching trailer lights directly to the vehicle's electrical system? If so, a ModuLite is required.

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Is the trailer being towed equipped with more that one light assembly per side? Does it have clearance lights, dual tail, turn or stop lights or any other equipment that will impose an extra load? If so, a ModuLite is required.

*

Is this the only trailer the driver will ever tow? Consider future requirements as well as current ones. In future applications, a ModuLite may be required.

Are There Other Ways To Determine The Need For A ModuLite?
Yes. Vehicle manufacturers caution consumers against adding additional loads to electrical circuits. Consult the vehicle owner's manual when recommending trailer wiring. The following are two examples from owner's manuals:

Jeep Grand Cherokee
"Do not connect a trailer lighting system directly to the lighting system of your vehicle. Use an approved trailer wiring harness. Failure to do so could damage the vehicle electrical system and/or result in personal injury."

Dodge Ram Pickup
"Towing a trailer equipped with more than the standard lighting (turn, tail, stop and back-up lamps) may cause an abnormally high electrical draw through the headlamp switch, causing the switch to fail."