Wer you running lipo?
if so the trigger contacts are likely fused together.
If not then there is likely a short someplace or broken/damaged trigger switch
Edit. Ahh yes the microswitch triggers forgot about those. Its likely that then. It could just be sticky from grime or corrosion if it was used in the rain or mud or stored in a damp area or even left over night in the car.
You could try sprayin the switch with some lube then blowing it off with some duster to remove any extra lube and gunk or replace the switch.
Not that i endorse evike that much but i think this is what yer after
http://www.evike.com/product_info.ph...ducts_id=25818