# trailer connector (truck side) question



## Earthscapes (Feb 2, 2001)

On my 90' and my old 02' i had a power wire to run the lights inside the trailer off the battery of the truck. It was the top right pin on a 7 pin connector. On my 03' i have no power on that pin. On the 02' i used the factory installed wiring harness and had power there. I used the same wiring harness from the 02' on the 03' (except i switched the 2 wires around like everyone said to) 

Question is do i need to run a wire from the battery to the trailer connector or is there an easier way to do it through the factory harness ? One more question there is a single (black) capped wire next to the connector what the heck is it for ? i have pulled the cap and tried to get power there but nothing happens.

Thanks,
Keith 

P.S. I'm ready for snow :waving:


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## Pelican (Nov 16, 2001)

I'm just guessing, but on my Ford's you have to install a fuse which is shipped in the glovebox in order to activate the hot lead to the plug. GM may be set up the same way. No info in your owner's manual?


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## wxmn6 (May 23, 2001)

Earthscapes - the black capped wire you described is for auxiliary backup lights. It is part of snowplow prep package. You just connect your aux. backup light to that wire and ur done. Of course, you still will need to ground the other wire on aux. backup lights for it to work.  

GM really messed things up with '03 trucks. To get power to the connector, you need to install a fuse that looks like a square. I don't remember but I think it is called booty. But I am pretty sure some part of it is discussed in your owner manual. 

In case if you didn't notice, there is labeling on the connector cover that tells you what each pin are for. It is a little hard to read, but still readable.


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## Earthscapes (Feb 2, 2001)

wxmn6----- so your saying if i pop the truck in reverse i'll get power to that wire.... cool thanks man. I guess that beats running wires to the back like i used to..

I read the "owners manual" 5 times and have found nothing. I know on the 02' i had to install a big square fuse for the trailer package... But there is not one shown for the 03'.

As far as the labeling goes.. i have read it and it shows a + mark for power at the pin i need power at,,,, like it should. 

This power wire it not a huge deal because we have been dealing with it all year so far,,,i'm just getting sick of firing up the generator to find the cooler full of   inside the dark trailer


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## wxmn6 (May 23, 2001)

Earthscapes - yes, when u shift to reverse, there will be power to that black capped wire. 

The wire for trailer connector power is already there all hooked up, but you just need to buy the fuse. A $2 square fuse and install it. Then your problem should be fixed. Using those generator would be a hassle, especially with the fact that the wire is already there waiting for you to put the fuse in the fuse box in the engine compartment. I do not remember which fuse size, but it has to be either 30A or 40A.


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## 75gmck25 (Feb 22, 2003)

*Re: 2003 GMC/Chevy trailer brake connector*

There is a service bulletin out on this - 
GM changed the pinouts on the trailer brake connector/adapter for 2003 - the one inside the cab where you plug in your controller.

If you plug in your old controller adapter (pre-2003)it will fit, but connect to the wrong pins. The scariest part is that it maps the running lights to the trailer brake pin. If you turn on the headlights, it activates the trailer brakes.
This is from Alldata
TSB: 02-05-22-004B Dated: OCT 02 Electrical - Trailer Brakes Applied With Headlamps ON


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## Earthscapes (Feb 2, 2001)

Ok i got it ........in the fuse box under the hood,, in the top left corner there is a red plug (dummy fuse) i put a 50 A fuse in there and now i'm all set and everything works great. 

Hey wxmn6 where can i find a connector to plug into the one for the reverse lights ?? no luck at the dealer.


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## Chuck Smith (Dec 30, 1999)

*Re: Re: 2003 GMC/Chevy trailer brake connector*



> _Originally posted by 75gmck25 _
> *... If you turn on the headlights, it activates the trailer brakes. *


Off topic, but I had a friend with a similar problem. He borrowed a truck from one of his friends to move a trailer. The truck was new (1989 F-350). He called me because the truck was on dirt, and he had over 5,000# on the trailer, and the Ford couldn't pull the trailer up the steep road to the paved road. He said the tires would just spin, and it was dark.

I went, hooked up, and dragged him and the trailer up the hill with my 77 Chevy. I felt bad but I told him before I did it I would spray the Ford with any loose rocks when going up the hill. I didn't spray him too bad...

He found out the next day that the trailer wiring was wrong, and when the lights were turned on, the trailer brakes locked. His friend neglected to tell him, because his friend didn't think he would be using the truck at night!

The sad part, is the guy who owned the truck and trailer was using it regularly, overloaded, with no working trailer brakes.

~Chuck


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## wxmn6 (May 23, 2001)

Wow - I guess that's why his friend truck just kept spinnin' and spinnin' .... hey that sounds like a F*rd!  

I just hope that guy don't travel around here without working trailer brakes!  I guess that is why NYS DOT are all over the places.  

Earthscapes - I don't believe that there is a connector for that black cap. It is just to cover the factory wire, so it won't come in contact to the frame and short out when you shift in reverse. Also to keep it from corrosion and dirt. 

I am yet to wire my aux. backup lights, and I intend to cut off that black cap and butt splice the wires together with dielectric grease inside it, then use dual wall heat shrink for waterproof seal. 

One more thing - I would replace that 50A fuse with 40A fuse. 50A does not give that much protection, especially for that wire size. If there is an overload or short, the wire would eventually melts before blowing out the fuse. You won't want to deal with that, do you?


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## BigRedBarn (Jan 4, 2003)

*Re: Re: 2003 GMC/Chevy trailer brake connector*



> _Originally posted by 75gmck25 _
> *There is a service bulletin out on this -
> GM changed the pinouts on the trailer brake connector/adapter for 2003 - the one inside the cab where you plug in your controller.
> 
> ...


I own a 2003 Silverado, and GM sent me a letter about how the 02 and 03 were wired differently in the trailer connector. They gave the number of a connector to use, but didn't say much about it.

I was wondering if anyone has info on this. Is there an adapter connector available which switches the pins around so you can hook up a 2003 pickup to a trailer without having to rewire the trailer? I often borrow a cousin's trailer, and I can't just rewire his trailer. And, I don't want to drive it w/o the electric brakes operating properly, or not at all. It would seem that an adapter would be the best solution.

I'm surprised I haven't seen more discussion of this in this forum. I've been keeping an eye out for info on this.


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## CT18fireman (Nov 30, 2000)

Are the actually pins at the back of the truck different? The 7 blade RV socket that most trucks come with these days has a standard wiring setup. Trailer manufacturers wire their trailers to fit this. I can't see why Chevy would decide to wire theirs different so that it would not work. I have seen individuals wire their own way and thus their trucks not work. I know Ford and Dodge set to the standard way of wiring. I thought the bulletin was for an adapter in the truck. Either way leave it to GM to screw up something as simple as trailer wiring.


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## wxmn6 (May 23, 2001)

No, the 7 pins trailer wiring is standard, nothing has changed. GM would never do that because if they did, alot of trailers would not work properly.

The problem with the '03 GM trucks is the *trailer wire harness* where you plug right under the dash for wiring to your brake controller. For some stupid reason, GM changed the location of two wires (pins) in the truck under the dash on '03 GM trucks. So that mean the harness designed for '01 and '02 GM trucks will not work properly if you attempt to use it on your '03. With proper instruction, you can change the location of two wires on the harness itself, or buy it from GM that is designed for '03.

Another thing that GM really screw up is that they did not include the harness on all '03 trucks. Alot of people complained about it and had to get it from their dealer or supplier.

The '04 GM trucks are coming up soon for ordering. So I have no way of telling which harness they will be using for the '04. I would image that it would be the same as '03 since it is same designed truck, and it would confuse people to make the switch again. This time they better include wiring harness in the truck.


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## CT18fireman (Nov 30, 2000)

Guess that is another reasone to buy a Ford. The traile brake connector comes right in the glove box. Splice your controller to it and plug it in. No problems. Why change things every year? Just confuses people and causes accidents. Someone at some point will switch the wires, think the have brakes or lights (yes they should check) and get in an accident. Then GM will see a big lawsuit.


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## wyldman (Jan 18, 2001)

The truck Mfg's should stick to a standard when it comes to this kind of stuff.Dodge had a similar problem with the brake controller wiring.They give you a nice connector,which plugs right in under the dash.Even has nice color coded wiring,which matches the wiring on the brake controller.NOT !If you connect everything up like you think it should go,like blk to blk,blue to blue,white to white,and red to red,it doesn't work,and will sometimes fry your brake controller.

The 7 Pin RV connector should be wired all the same,as it is a standard for all trailers.

We see quite a few plugs,and trailer ends wired up wrong,as people do there own wiring,and don't adhere to the standard.

If you can't find the correct plug for the reverse light feed,just cut it off and use a weatherpack connector.


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## wxmn6 (May 23, 2001)

GM is just causing everyone a hassle with their '03 trucks. Why buy a $30-40K truck and deal with inconvience? Another few things that GM removed from their '03 model line is the under hood light, under dash light, mold trim along the truck bed. (come to mind, Dodge and Ford don't even have mold trim either)

You are right, GM could be seeing some lawsuits. I heard a story about a guy who was pulling a triaxles trailer through underground tunnel. It was his first day pulling after he bought a new truck and installed a wiring harness that is supposed to be for '01 and '02. At this point, he did not know that the '03 truck use different harness. When he went in the tunnel, his automatic headlights turns on, and that caused the trailer brakes to activate. His trailer tires were squealing but fortunately his Duramax has plenty of power to get through the long tunnel then pulled over once he got out of tunnel.  That Duramax has some serious power!


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## wyldman (Jan 18, 2001)

You'd think some of these guys would check the trailer lights\brakes BEFORE they get out on the road.If your hauling a tri-axle (which must have something heavy on it),I'd never even pull away without checking my trailer brakes.No brakes,no tow.That's just plain stupidity.


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## wxmn6 (May 23, 2001)

I know. When I installed my brake controller in my truck, I tested all trailer functions once the completion of installation. I want to make sure everything is working properly before my first tow with the truck. 

It is a shame that alot of people do not take towing trailers responsibility seriously. I have seen many people towing trailers that is in poor shape. Some tires are worned out, missing lights, no safety chain, non working break away system, no power coming into trailer to charge the battery for break away system, brakes not working or not properly adjusted. Those people think it is no big deal. :realmad:

A little bit off topic but ....Last year, someone was towing a small 4'x4' trailer WAY OVERLOADED with top soil on the road I was working nearby. All of sudden I heard a loud POP, turned around, saw road full of smoke. Once the smoke cleared, I saw a Jeep pulled over the road with a blown tire on the tiny trailer. Driver came out, looked at it, then just drove away.


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## wyldman (Jan 18, 2001)

It's funny you brought that up,I see it all the time.People buy these little 4' trailers cheap,and put a huge box on them.Usually you see them in the spring,with a couple of yards heaped on it.Not pretty seeing a trailer rated for 800 lbs,with a few tons on it,being towed by a Toyota Echo.I really wish they would mandate a trailer or towing safety course to be able to tow a trailer,so these idiots may have a clue what they are doing.


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## CT18fireman (Nov 30, 2000)

You know what I think is worse? The fact that people can go buy an RV longer than a truck and drive it off the lot with no training. Add the fact that most of the drivers are ederly and it becomes a problem.


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## Arc Burn (Oct 21, 2002)

OK CT,you went off topic and i'm gonna follow 
Not picking on you at all because your a fireman but i think that worse than the RV's are the local fire departments letting young guys(or any guys) drive some of those rigs with no CDL,just get in it and go,thats how it is around my area anyways and i know some of these guys,trust me,they shouldn't be driving cars let alone heavy trucks like that.

BTW-These are volunteer dept's that i'm speaking of.


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## CT18fireman (Nov 30, 2000)

Does not happen in CT. Maybe in NY. 

Here you need a class Q which is a CDL driving test without the written part. You only need to do the walk around, parking, and over the road test.

Many of our operators get the CDL to have it.

Beyond this most departments have drivers go through extensive practice and supervised runs before getting to drive alone.


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## Barkleymut (Jan 10, 2000)

It blows my mind that I can drive an ext.cab long box truck with a 27' trailer behind it with zero experience. I measure around 48' total. That is darn close to being as big as a semi's trailer.


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