i have a crown pe4000 double pallet truck and at first it would not reverse so i started with the cheapest thing and replaced the reverse switch. that didn't work. so i tested the accel pot and everything seems fine but i now have no travel forward or reverse. the only time that it will move is if you hold down the (sas) safety switch. could the wiring harness be bad and how do i test or tell if it is. any help will be greatly appreciated because i'm fairly new at fixing forklifts.