Have a amigo smart shopper scooter and "dead man" switch apparently not working correctly. When I depress thottle, scooter goes forward without any weight on seat?

Have you had it for some time or did you just get it. If it was working and now it is not, you most likely need a new switch. If you just got it, it is possible that the previous owner bypassed the switch. Look under the seat and see if the wires are connected to the switch. If they are not connected, connect them to the switch. If they are connected, you need a new switch.

Need to know how old unit is smart shoppers now use seat switches that are normally open without weight and when seated normally closed, if you unplug the wires that come from the seat switch and the cart doesn't move then the seat switch is stuck and should be replaced. older units were normally closed without weight and normally open when seated in this case check to see if the wires have come unplugged and reconnect them then recheck if cart won't run when seated replace seat switch.