The tail lights on your Jeep Grand Cherokee are not hard to change or to test. Some Grand Cherokees have an issue where the tail lights go out at night when the brake lights go on, and then come back on when the vehicle is in motion again. That problem is beyond the scope of this article, and requires slight modification of the bulb socket itself.
Bulbs
Sometimes, the problem is just as simple as a burnt out light bulb. Remove the tail light lens with a Torx style screwdriver. The bolts are accessed from inside the cargo area of the Grand Cherokee, to the left and right of the open hatch door. Inside the housing, you will find a row of three bulbs lined up vertically. The top bulb is the Grand Cherokee’s brake lamp, the middle one is the tail light and turn signal, and the bottom bulb is the reverse light. Grab the middle bulb and twist it counter-clockwise to remove it. Inspect the filament inside the glass. It should look like two metal prongs with either one or two thin, squiggly wires connecting in the middle. If a small, squiqqly wire is broken, then the bulb is no good and it will need replacing. The thin wires are the ones that glow when power is applied to the bulb. Without them, they cannot shine.
Power and ground wires
Check both the power and the ground wires that connect to the bulb socket to make sure they are in one piece and connected well. The power wire is usually the culprit. It should be free of any damage or major kinks, and should be fully sheathed in plastic. With the running lights of the Grand Cherokee switched on, ground the test light and touch it to the power wire where it is accessible at the socket connection The indicator should light up, assuring us that there are twelve volts of electricity reaching the connection. If it does not light up, the bulb is not getting power and the red wire is damaged somewhere. The ground wire should also be free of tears and major kinks, but should not have any power to it. If the ground wire is bared in places that is okay, because it isn’t “hot”, meaning it isn’t carrying any current. Just make sure it isn’t loose or broken.
Fuse Failure
Under the passenger side of the dashboard in the kick panel of the Grand Cherokee, you’ll find the fuse panel. Remove the cover to it and find the fuse that is labeled “Park/Tail” and remove it. Inspect the thin wire inside that connects the two prongs. If it is broken, then the fuse has been compromised and requires replacement. Only use an exact replacement fuse, which in most cases is a 20-amp unit. Do not try to put in a smaller or larger amperage rated fuse. There isn’t a special type fuse specifically for the Jeep Grand Cherokee, so they can be purchased at the local auto parts store without an issue. Once the fuse has been replaced, test the tail lights to ensure that was the only issue.
