Sparrow / NmG
The accelerator in a Sparrow sends a signal to the motor controller via a "pot box," where "pot" is short for potentiometer. The part in a Sparrow is a Curtis PB-6, which contains a microswitch that positively identifies the "foot up" position and a pot that reads between 0 and 5K ohms. The Curtis PB-6 isn't known for reliability, even if it is commonly used in golf carts, so it's a part that is commonly replaced in a Sparrow. You can replace the entire box, pretty easily, or you can replace the pot inside it with a high-quality sealed unit. The only requirement is that it read between 0 and 5K ohms in about 90 degrees of swing. Here's a few pictures for reference.
The original pot is part number PMC98191. It appears to be a custom range pot made for this application. I have found them on the web listed from about $19-$35 (Sep 09).
Pot Box, partially removed
Microswitch wires, as they surface in the high-voltage compartment
These two wires will comprise a short when the accelerator is pressed and an open circuit when the pedal is entirely up.
Accelerator Pot Wires, as they surface in the high-voltage compartment
These two will show some resistance between 0 and 5K ohms.