When I purchased my '01 2500hd, the wiring harness was rolled up and placed in the passenger side door pocket. It had a white tag tied to it with instructions explaining what each wire was to be connected to. I had to look in the owners manual to get more info as to exactly where the plug was to be connected in the courtesy center below and to the left of the steering column.
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system