Haha, are you serious ? its prewired ?, and what do you mean by main harness. I just bought the fog light kit from mars warehouse earlier today :P :( But atleast it comes with the relay, the lamps, screws, and push switch ( didnt want the oem stalk ) So now tomorrow i'll just order the shrouds / plastic covers. Yeap, have you ever looked behind your bumper? The main harness with the foglight connectors are already there. So that means everything in the engine bay side of things is already done except for the 2 lamps and H11 bulbs. You don't need to run any cables through the firewall. Inside the cabin, you need to install the relay, which is on a fusebox behind your A/C dials. So you need to remove the side trims, remove the air vents, and pull out your headunit before you can reach behind there. I'll email you the official Toyota manual for aftermarket fog kits. PM'd.