Chevy trailblazer trailer lights round connector problem

ggundersen3

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
246
I had a 2004 Chevy trailblazer with no trailer light problems at all. Always worked correctly. I recently traded it in and bought a 2008 trailblazer. With this one,something is wrong with the round connector on the vehicle. There is power but the pins in the connector don't line up correctly with the GM diagram of which pins should be ground, tail / running lights, left and right brake and turn signal, Etc. Its like its miswired, thus there is no power at the pins on the flat 4 side of the adapter. Im at a loss.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
There are probably fuses you need to add to the fuse box. Look in your manual.
 

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
Bruce is right, if that connector has never been used before, you have to install the fuses for the connection, check your owners manual and it should let you know what needs to be done.
 

ggundersen3

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
246
Ill check again but i believe i did that when i in first discovered this problem and the trailer light fuses were all there. Like i stated, i tested the pins with a test light and there is power at the pins in the connector but it appears they seem out of order meaning they don't match up correctly with the GM diagram. In fact for example 2 different pins
 

ggundersen3

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
246
In fact 2 different pins had power and flashed with a turn signal. Seriously. Its like the connector is damaged or shorted or?? Frustrated
 

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
Well if you have a shorted out connector, you will need to secure a replacement for it and plug the new one in underneath the back of the Trailblazer. Does it have the factory wiring or does it have an aftermarket Hopkins, Curt, etc.connector? You can get a new T-connector harness from the auto parts store for less than $30 bucks.

I had to replace mine the other day, went out to plug the boat trailer in and no ground pin, somehow it got broke off over the winter.
 
Last edited:

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
Its factory GM.

No big deal, they sell replacements at most of the major parts store, and I know for a fact that Hopkins makes the ones GM includes in their towing package, but it is less expensive to buy it at the parts store.
 

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
After years of fiddling with lights on various trailers, I finally gave up and normally figure I am going to have to replace connectors at least once a year, when dealing with factory stuff, I have found it much easier, just to un-plug and plug a new harness in. When they started putting computers in cars, it became much more difficult to tap wires because you never know which wire is being monitored by that computer and it often times leads to check engine lights coming on. My buddy tried to work on his and ended up burning the computer up in his Nissan truck, that was a very expensive lesson to learn.

If you have two pins lighting up with the turn signals, you have a short in that system somewhere or you could just have one that was wired wrong from the factory, that does happen, also pins get hooked up wrong in the plug when they are molded, do you have the factory color coded GM wiring diagram for the year you are working on? Make sure you have the correct one, because all of the companies have a tendency to change colors on their wires over the years.

Another thing, I was just checking some of the manuals I have, did you make sure that the maxfuse is installed so the power lug under the hood has power, some of the later model GM vehicles came with a blank fuse installed where the 40 amp maxfuse needs to be installed. Do you know if the previous owner towed with this vehicle?
 
Last edited:

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Wonderful Forum! Not trying to hijack but I was having trouble with the RH turn/stop on my Silverado. After trouble-shooting the trailer, you guys clued me in to the under hood fuses. Blown 10 amp. Problem solved. Thanks.
 

ggundersen3

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
246
Thanks everybody for all your help. Well it appears corrosion of the contacts may have been my problem. I unplugged the vehicle harness that plugs into the connector and plugged it back in several times. Then hooked up the trailer,plugged in the 7 to 4 adapter and now all lights are working correct. I hope the problem doesn't return.
 

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
If you had corrosion, then pick up some dielectric grease and put in the plugs, that will help keep the corrosion from coming back.
 

madmathew

Cadet
Joined
Jun 9, 2015
Messages
13
There is a tester that you can plug in to the plug on the truck and it will show whether the plug works correctly or not. The auto parts or Harbor Freight will have the tester.
 

MTboatguy

Fleet Admiral
Joined
Jul 8, 2010
Messages
8,988
There is a tester that you can plug in to the plug on the truck and it will show whether the plug works correctly or not. The auto parts or Harbor Freight will have the tester.

Problem was fixed almost a month ago.
 
Top