DIY, change the 8-pin trailer harness connector on your GMC Sierra. The replacement process described next is similar on most GMC trucks and SUVs and the only tool you’ll need is a small flat headed screwdriver. In some cases you might need some penetrating oil or a similar product to apply on the metal, behind the connector. This repair is simple and it won’t take you more than 15 minutes.
First of all, you should get underneath the back of your truck and you should disconnect by hand, the connector shown in the image below. This connector has a safety tab that can be pressed with your thumb, then it should come out easily. If you have trouble with these parts, you can use some penetrating oil to grease them a little and make them easier to remove.
After you do it, you can move to the exterior side and, using a flat headed screwdriver, you should push on the little tab shown in the picture below. This will unblock the 8-pin connector, receptacle, that can be removed by twisting it counterclockwise.
Now make the required replacements and repairs and reinstall the new parts back, by reversing the whole process. These are the steps you need to follow, if you wish to remove and replace the 8-pin trailer harness connector on your GMC Sierra, manufactured between the years 1999 and 2006.