The control switches are a rheostat which 'dims' the voltage to give the rider a better control of the battery power to the motor, particularly when manoevering at slow speed in confined spaces.
Your control switch (rheostat) is either burnt out at the Hare setting or the contacts inside could just be tarnished if water/damp has got inside the switch.
It is possible to bypass the rheostat completely as a short term measure. Just connect the rheostat input to the output cable. The scooter will perform is if it is permanently in the Hare setting- so be carefull!
Geoff in Wales with a Stirling Gem
September 2010