Trailer Harnass Voltage

LGillingham · March 8, 2008

I have a 2003 Sierra 2500HD and recently discovered when I hooked up my utility trailer that I didn't have voltage for the brake lights on the receptical for trailer supply. I checked with a local trailer dealer and he said that the 03's had a common problem with the "clock spring" located in the steering column. Has anyone had a similar issue and how did you deal with it? Does GM have any recall on this? Is there an adapter for the chasis wiring to supply the trailer similar to what was done on older model trucks?

outlawfab · March 8, 2008

check your fuses.

LGillingham · March 9, 2008

check your fuses.

I've done that and so has the trailer dealer and all looks ok. The trailer dealer seems adament that it is the clock spring, says he has seen many 03's with the same issue. So I figured I'd try and find someone who has actually had this issue. The trailer dealer also tells me that there is no adapter for connecting the trailer harnass to the chasis wiring but I did find an online document where it references such a beast and again I was wondering if anyone had experienced this one. It seems to be a cheaper alternative than having the GM dealership spend countless hours (on my dime) replacing the clock spring. As well, I have noticed that my truck is not going into the tow/haul mode when I press the switch. Any suggestions on this one? Thanks.

sonjaab · March 10, 2008

Did you check the truck trailer plug pinouts with a test light?

Remember GM changed the pinout arraNgement in 03.

My plug set up wouldn't work with the old plug set up from my

01 when I used it on my 04. I had to change the pin outs.

Also note the aux. power pin won't have power till you put a

maxifuse in either stud #1 or #2 (forgot which)...............

GM quit putting a fuse in when they eliminated the underhood light

and other stuff in 03 or 04.

I had to install the fuse to power the pin and the aux. light set up

in my 04.....................

LGillingham · March 10, 2008

Did you check the truck trailer plug pinouts with a test light?
Remember GM changed the pinout arraNgement in 03.

My plug set up wouldn't work with the old plug set up from my

01 when I used it on my 04. I had to change the pin outs.

Also note the aux. power pin won't have power till you put a

maxifuse in either stud #1 or #2 (forgot which)...............

GM quit putting a fuse in when they eliminated the underhood light

and other stuff in 03 or 04.

I had to install the fuse to power the pin and the aux. light set up

in my 04.....................

Hey Sonjaab,

All these items have been checked both by myself with a multi-meter and the trailer vendor with his test equipment. The thing is that this hook up was working fine a couple of months ago when I used the trailer last. I've been doing some reading on this forum and it seems that some people have had a similiar issue and have traced it to the hazard light flasher. After some contorsionist acts this morning I managed to remove the one on my truck and it appears to be a special application for trailer packages. I went to the GM dealer and a new one costs $100 - alot of money to pay for a part you are not sure is the correct one and is non-returnable. Then I talked to one of those so called 'service advisored' and he expressed criticizim over this being the source of the trouble. After further conversation with him I realized he didn't know his elbow from his a**o so it is difficult to rely on information from these people. I count more on the opinions and experiences from people here on this forum. I guess I may have to bite the bullet and purchase the part and hope for the best. Thanks for your input.

outlawfab · March 10, 2008

if i remember correctly there are 2 fuses in the dash fuse panel on the left side which have fuses for the trailer stop lamps. also that expensive flasher i believe converts stop and turn which is seperate bulbs on the truck to a single feed on the trailer.

LGillingham · March 11, 2008

if i remember correctly there are 2 fuses in the dash fuse panel on the left side which have fuses for the trailer stop lamps. also that expensive flasher i believe converts stop and turn which is seperate bulbs on the truck to a single feed on the trailer.

Yes, the fuses are there and determined to be ok and I do believe that you are correct regarding the hazard light flasher. It is noted on the flasher that is a component of the trailer package. The weird thing today is that after I had removed this part, visited the dealer where I was told that this was unlikely the cause, returned home and fitted the part again, there was voltage on the trailer brake light harnass. I don't know if I had a bad connection,an intermittent problem in the flasher or a problem elsewhere. I guess I will monitor for the next couple of days to see if it changes...spending $100 for a part just to try may be the next move...a hundred dollars won't buy me much troubleshooting at the dealership.

countryboy1365 · March 11, 2008

Also note the aux. power pin won't have power till you put a
maxifuse in either stud #1 or #2 (forgot which)...............

GM quit putting a fuse in when they eliminated the underhood light

and other stuff in 03 or 04.

I had to install the fuse to power the pin and the aux. light set up

in my 04.....................

not to post jack but is that true for the 07-08 if so is that the fuse block under the hood?

sonjaab · March 12, 2008

YUP............With the GMT-900s you need to put the maxi fuse in

the UNDERHOOD box Stud #1 to power up the aux. power wire in

the trailer connector.

Which by the way is the center pin !

Check the diagram here:

http://www.stealthv.com/images/GMT900_Trai...ler_Install.pdf

pg.20

NOTE this diagram from Marks RV

http://www.marksrv.com/wiring.htm

It is different !!!!!!!! It shows the center pin as back up lights!

and the pin out is different .

I think this is where Lawson is having problems !!!!!!!!!!!!

Like I will say AGAIN!!!!!!!!..............GM changed the pin out in 03 !!!!!!!!!!!

LGillingham · March 12, 2008

YUP............With the GMT-900s you need to put the maxi fuse in
the UNDERHOOD box Stud #1 to power up the aux. power wire in

the trailer connector.

Which by the way is the center pin !

Check the diagram here:

http://www.stealthv.com/images/GMT900_Trai...ler_Install.pdf

pg.20

NOTE this diagram from Marks RV

http://www.marksrv.com/wiring.htm

It is different !!!!!!!! It shows the center pin as back up lights!

and the pin out is different .

I think this is where Lawson is having problems !!!!!!!!!!!!

Like I will say AGAIN!!!!!!!!..............GM changed the pin out in 03 !!!!!!!!!!!

Thanks for the information. My arrangement is as per the diagram you provided. The problem on my truck is intermittent. All of those connections are live at the time they are suppose to be with the exception of the brake lights. I have been able to get voltage back on the brake light connections sometimes by removing and fitting again the hazard light flasher other times by switching on and then off the turn signal. Sometimes I will get voltage only on one side and other times both sides. For this reason I am prone to think the source of the trouble is this flasher relay. If anyone has any thoughts or suggestions I would love to hear them.

I have an update on this situation. Today I purchased the hazard flasher from GM (although the parts rep and service advisor assured me that this was not the source of the problem) and fitted it. I now have voltage for the brake lights for both sides on the wiring harnass consistently. I have attached pictures of the culprit component but be advised that the GM part # indicated on the part has changed to #10383321. I hope this is of assistance to anyone else with similar issues and I would like to extend my gratitude to all who offered advise on my posting and to others who posted their experiences on this site, it has allowed me to resolve one issue with minimal contributions to the GM bank account. By the way, this component cost me $118 including the governments portion.

LGillingham · March 15, 2008

YUP............With the GMT-900s you need to put the maxi fuse in
the UNDERHOOD box Stud #1 to power up the aux. power wire in

the trailer connector.

Which by the way is the center pin !

Check the diagram here:

http://www.stealthv.com/images/GMT900_Trai...ler_Install.pdf

pg.20

NOTE this diagram from Marks RV

http://www.marksrv.com/wiring.htm

It is different !!!!!!!! It shows the center pin as back up lights!

and the pin out is different .

I think this is where Lawson is having problems !!!!!!!!!!!!

Like I will say AGAIN!!!!!!!!..............GM changed the pin out in 03 !!!!!!!!!!!

Thanks for the information. My arrangement is as per the diagram you provided. The problem on my truck is intermittent. All of those connections are live at the time they are suppose to be with the exception of the brake lights. I have been able to get voltage back on the brake light connections sometimes by removing and fitting again the hazard light flasher other times by switching on and then off the turn signal. Sometimes I will get voltage only on one side and other times both sides. For this reason I am prone to think the source of the trouble is this flasher relay. If anyone has any thoughts or suggestions I would love to hear them.

I have an update on this situation. Today I purchased the hazard flasher from GM (although the parts rep and service advisor assured me that this was not the source of the problem) and fitted it. I now have voltage for the brake lights for both sides on the wiring harnass consistently. I have attached pictures of the culprit component but be advised that the GM part # indicated on the part has changed to #10383321. I hope this is of assistance to anyone else with similar issues and I would like to extend my gratitude to all who offered advise on my posting and to others who posted their experiences on this site, it has allowed me to resolve one issue with minimal contributions to the GM bank account. By the way, this component cost me $118 including the governments portion.

Just for info.

sonjaab · March 15, 2008

WOW Neu..............Thats the first time I have ever heard of that flasher

relay causing a problem like that !

Glad to hear its fixed!

LGillingham · March 15, 2008

WOW Neu..............Thats the first time I have ever heard of that flasher
relay causing a problem like that !

Glad to hear its fixed!

I had done a search in this forum and found another person who had had a similiar issue. They had GM do the trouble shooting and found it to be this component. I also found a wiring diagram on here which indicated that this component was in the circuit and that's how I started looking here. I had to take the trim around the dash gauges off and the section of the dash below the steering wheel off to access this part. It is not easy to locate even if you know it is there, it actually plugs into the back side of the fuse panel. I guess it would have been too simple to have it on the same side as the fuses. My six year old son thought it was rather amusing driving around for the past week with several parts of the dash sitting on the back seat. I'm sure glad I found this forum.

monker · March 16, 2008

Glad you found the problem. I went through the same thing back in January, but with only 1 brake light. Really had my stumped since all the trailer signals still worked. I never suspected the flasher unit but that's what it was. Apparently all the trailer lights go through there.

LGillingham · March 16, 2008

Glad you found the problem. I went through the same thing back in January, but with only 1 brake light. Really had my stumped since all the trailer signals still worked. I never suspected the flasher unit but that's what it was. Apparently all the trailer lights go through there.

You're not the only one stumped by this one. A local trailer dealer was surprised to find what the cause was and he had his technicians come out to my truck so that I could explain it to them. He certainly appreciated it as people tend to come to them first as opposed to the GM dealer. As well a local automotive parts supplier in my area was surprised to find out the cause and asked me to stop in and let him know when I was sure of the results. Then of course there is the GM technicians who told me that this was definitely not the cause. I didn't go back to them as I suspect they won't believe me anyway. Fortunately for me someone had entered their similar experience in here and that was a big help. Just as a point of note, my light troubles also was initially on one brake light then intermittently on both. I could remove this flasher and fit it again and get different results.