This is the 5K Ohm RVQ28YSH 25F S502 throttle potentiometer from TOCOS. This potentiometer (or "throttle pot") is used especially by Golden Technologies for their Companion series of mobility scooters.
The throttle pot is also known as the engager or throttle switch. Faulty throttle potentiometers can lead to "jerky" motion while throttling, or no motion at all.