Are you saying that it doesn't stop when it takes up pressure? if so, I had a similiar problem there is a grub screw on the pump that needs to be wound back a half turn to make it stop on pressure.
If you can't find the pump switch I think there are 3 possible locations:
1: Drifter control panel - one switch is the battery and one is the pump.
2: Coast control panel - one switch is battery voltage and the other is water pump.
3: If you don't have any control panel there can be a switch the same as a single light switch in a house, usually located near the gas HW switch, but has been known to be installed anywhere... if you need pictures let me know.
Hope one of these helps your situation