Exactly. Use the VW adaptor harness that you can buy at Best Buy or order online. It is basically as easy as matching the wires from the stereo to the harness crimp them and plug and play. How I did mine was to drop the radio box down off the cab and mounted the stereo in it and then plugged everything up and used one of the 4 mounting bolts for my ground, because the ground they give you sometimes does not work. The speakers are already up in there, but I switched mine out to Polk Audios. The are much brighter and sound much cleaner than the paper ones they put in there. I put an Alpine head unit in it with a USB port and a 1/8th inch stereo in plug. It cost less than 100 bucks at Best Buy. It is was rated at 25watts/channel, but it probably only has 10 which is enough in that tractor. It sounds great. I was using my iPod in there, but it was always bouncing around, so I just a 2 gig jump drive and loaded it full of music and I leave it in there all the time and never misses a beat.
Good luck. Let us know how it goes.