To answer your questions..
(Remember my ML is a '98...just in case there are some differences.)The plug for the foglights is back behind the drivers side headlight (between it and and the windshield washer reservoir). It was tucked way back in the corner and hard to find, but when I pulled it out, it was clearly labeled 'Fog & Aux lights', with a sticker. The wires were short (which made it hard to work) and there were only 2 of them with a dead-end plug. Since I was wiring 4 wires from the after market fog lights into the 2 factory wires, I cut the factory plug off and found an adaptor for 2 into 1. The mounting of my lights and directing the wire to this point was easy. Attaching my 4 wires to their 2 was the hard part as there isn't much room in there for the 2 hands needed to do the work (I tried to remove the reservoir, but decided to exercise patience instead). Of course the lights will not work if you don't have the factory switch activated by the dealer (I don't remember the exact cost as I had this done sometime ago, around $50.00). I'm sure there are other approaches to this, but that's my story and I'm sticking to it. Have fun...oh, and don't forget to aim your lights accordingly.