You should be able to tell the difference just by looking at the lights while in operation. Halogen lights are your typical or standard warm yellow light. HIDs can vary greatly in color but they are typically much much cooler, brighter light. They can appear almost white or often bluish or purple looking. HIDs would also require a small electronic box called a ballast on each side. You should be able to see wires running from the back of the housing to the ballast if it’s there. If the previous owner has left the stock halogen setup in place, you should be able to swap in any halogen replacement housing very easily. If it has been converted to an HID setup, you will have some decisions to make about whether to keep the setup or go back to halogen.

If I’m telling you things you already know, my apologies. I hate to assume what someone does or doesn’t know so I typically default to assuming they are still learning. We all had to learn at some point, lol.

I would post a photo of the output, and wiring if you still have trouble figuring out what you’ve got. If they are HID, you should also hear a buzz or hum with the lights on and truck off. At least on initial power up.