Will this mount to the factory cab light location?

Yes. This assembly is designed for the factory mounting points on second-gen Ram cab lights. You won't need to drill or modify—it bolts right in where the original sat.

Do I need to replace the wiring, or does it use the existing harness?

The bulb plugs into the existing factory socket. If your truck's cab light wiring is intact, you're ready to install. No rewiring required.

What's the advantage of LED over the stock incandescent bulb?

LEDs last significantly longer and draw less current. You'll get brighter, warmer light that won't dim or burn out like a filament bulb—especially useful if you're running aux lights off a heavy electrical load.