The first thing you will need to flat tow your 1999 GMC Jimmy 4WD, is a base plate kit. The Roadmaster Base Plate Kit, part # 179-2, is the correct choice for a base plate kit if your Jimmy is not a Black Diamond, ZR2 or an Xtreme. The kit has a simple installation with no welding required. I have linked the installation details for you to check out.
For a tow bar, I recommend the Roadmaster Falcon 2 Tow Bar, part # RM-520. The quick-disconnect system lets you quickly and easily mount... view full answer...
If your 1999 GMC Jimmy does not have a round U.S. Car connector tucked up under the bumper or spare to allow you to plug in a part like # 118384, or a bundle of wires you can connect to a 4-pole part like # HM41225 you can still install a trailer harness by splicing to the signal wires at one of the tail lights.
The best option is to hard wire a universal powered harness like # C59496 which will isolate and protect the truck's wiring from any potential shorts on the trailer. This is a... view full answer...