Here are my two cents--several folks have stated there are spare wires but short of finding someone at WRV to tell you exactly where they terminate, it was overwhelming for me to look on both ends of the harness to find "SP1 and 2". So I just ran a wire back thru the basement--its a bit difficult to find entry and exits to/from the basement but it can be done for one wire--ie, back corner of the propane tank area for entry and beside the rear bedroom heat vent for the rear exit...
Remember that you must also tap into the brake-light on/off switch cable located below the driver's seat area and inside the wheel well. My 03 40ft allowed me to run these wires down/inside the steering column and thru the floor by the brake pedal.....good luck....dean
2003 40' MDTS
Garden Ridge, Texas