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Mark Shaw

GM's 7 Way Trailer Plug Auxiliary Not Connected

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Yesterday, I learned why my inside lights on my new enclosed trailer didn't work.  Evidently, GM does not connect power to the auxiliary wire (center contact on the plug) at the factory.  The service man at the trailer dealer showed me that under the hood between the fuse box and the trailer brake control unit, there is a red wire with a loop connector coiled & taped off.  That wire must be connected to one of the two posts provided at the front of the fuse box to activate the center auxiliary connection on the trailer receptacle that operates the inside lights on most trailers. 

 

I asked him why GM would not make this connection?  He thought it was so GM dealers could charge a service fee to prep GM vehicles for towing.  It took less than two minutes to connect the wire and locate a 10mm nut to fasten it to the terminal.  

 

We checked the owners manual, and sure enough, it says:

 “It should be installed by your dealer or a qualified service center.”

Edited by Mark Shaw (see edit history)
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This comes up all the time on a GM truck forum I help moderate.  Seems silly to me, but I'm not in the business of trying to confuse customers.

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What year is your truck, Larry? I was just wondering two days ago why the interior lights of my trailer don't work when hooked up. I was thinking I'd have to rewire it to connect to the running lights or something. So glad I caught this thread!

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A friend of mine is a GMC truck dealer owner and I believe he told me so  that they can explain to the customer that the circuit is fused and to have the customer be aware of the limitations.  I have had to attach that wire on 3 tow rigs!  I also charge my two trailer house batteries with that circuit but haven't popped the truck fuse yet! When using my winch I always start the truck to be certain all the power I can get is available to the winch motor.

Robert

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My 2006 Silverado power pin on plug was dead until I added the missing fuse to the box under the hood.

All wiring was in place, yes I was surprised GM didn't spend the price for an fuse.

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Matt, my work life was with GM and Chevrolet.

The FACTUAL reason the battery feed wire is not connected .....  is to disarm a  LIVE battery feed terminal, at the  plug connector, IF a live 12 volt feed is not required, by the customer.

This practice has been in effect, going back to 1975, for certain.

Under normal travel trailer hook ups, the TRALIER BATTERY would supply the 12 volt requirements for the trailer,   while the red, LIVE wire would serve as the charge line for the TRAILER BATTERY, when trailer is being towed.

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On ‎1‎/‎31‎/‎2018 at 3:55 PM, bobg1951chevy said:

The FACTUAL reason the battery feed wire is not connected .....  is to disarm a  LIVE battery feed terminal, at the  plug connector

 

It is also a fact that the vehicle connection is the female side and poses virtually no risk to the owner unless the trailer wiring is incorrect.

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7 hours ago, Mark Shaw said:

 

It is also a fact that the vehicle connection is the female side and poses virtually no risk to the owner unless the trailer wiring is incorrect.

The trailer wiring plug connector, on the VEHICLE,  has the MALE connectors, the wiring plug connector, on the TRAILER,  has the FEMALE connectors.

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I have never ever seen male connectors on a vehicle.  I suppose a real dumb amature who didn't rad the instructions could do it that way.  It would be dangerous.  If the connector touched anything or anything touched it you would/could have a short.  The male connector should always be on the towed unit.

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1 hour ago, bobg1951chevy said:

The trailer wiring plug connector, on the VEHICLE,  has the MALE connectors, the wiring plug connector, on the TRAILER,  has the FEMALE connectors.

 

I believe we are both right.  The pins on the vehicle side are male, but they are recessed within the plug receiver and covered when not in use. 

The male trailer plug (with the female pin holes) fits well inside the connector receiver.

 

s-l1000.jpg

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1 hour ago, Tinindian said:

I have never ever seen male connectors on a vehicle.  I suppose a real dumb amature who didn't rad the instructions could do it that way.  It would be dangerous.  If the connector touched anything or anything touched it you would/could have a short.  The male connector should always be on the towed unit.

It doesn't work the way you would like.

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28 minutes ago, Mark Shaw said:

 

I believe we are both right.  The pins on the vehicle side are male, but they are recessed within the plug receiver and covered when not in use. 

The male trailer plug (with the female pin holes) fits well inside the connector receiver.

 

s-l1000.jpg

 

Again, the male connector is on the vehicle side, not the trailer side.

Let's move on.

The point is, with the red power / battery lead connected under the hood, the 12 volt wire  is live  ..........  through the vehicle and back to the vehicle connector.

If that live blade was to be damaged / interrupted, a short or spark or fire could follow.

If the live 12 volt wire, itself,  was damaged, in any way, going from under the hood to the rear bumper,  the same issues could be the end result.

So ..... to lessen the chance of unwanted problems, CHEVROLET left the live wire unattached, unarmed..

The owners manual addresses  the 12 volt hookup, if towing with all 7 blades is needed. .

Some towing situations only require a 4 blade connection, allowing the 12 volt power line to remain unarmed.

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On ‎1‎/‎31‎/‎2018 at 3:18 PM, huptoy said:

My 2006 Silverado power pin on plug was dead until I added the missing fuse to the box under the hood.

All wiring was in place, yes I was surprised GM didn't spend the price for an fuse.

 

I have read that about 1/2 of all truck sold have never been attached to a trailer.

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2 hours ago, Larry Schramm said:

 

I have read that about 1/2 of all truck sold have never been attached to a trailer.

True ....... at least with Chevy figures.

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