Got yourself a really fancy GPS eh? All right!
A 2000 chassis may not have the VSS signal wire you are looking for. I'd call Spartan and ask them first hand. Another thought is if there is a way to disable the VSS input from the GPS setup menus and thus let the GPS track speed from the satellites - the good old fashioned GPS way? That might be another option for you.
From
Spartan Chassis | Everything's Riding On It.
Recreational Vehicle Customers Only:
Customer Service 800.543.4277 (Option 1)
7:00am - 11:00pm/7 days a week