ElectricScooterParts.com Support Center

I found an electric scooter throttle with Red, Yellow, and Green wires and tested it to determine what the functions of the wires are and found that Red is +5V input, Yellow is ground, and Green is the output signal wire.

The throttle I tested is not from a Schwinn Missile FS so I cannot 100% confirm that your throttle and my throttle are wired identically, but chances are very high that they are. I also found an old throttle to controller service bulletin that showed Yellow as being the ground wire on three wire throttles.

I found a way to non destructively test the throttle's wire colors. With a variable DC power supply I applied +5 Volts to the throttles Red wire. Then I set my multimeter to DC Volts and connected its Black ground probe to the power supply's Black ground output, then with the multimeter's Red positive probe I tested the Voltage of the throttles remaining two throttle wires. What I found was the throttle output signal wire has around +4.5 Volts present, and its ground wire had around +5 Volts present. I tested a standard three wire throttle with Red, Black, and Green wires to determine this, then I performed the same test on the throttle with Red, Yellow, and Green wires and got identical results. So next I took an educated guess that the Yellow wire was ground and tested the Red Yellow Green throttle with +5 Volts to Red, Ground to Yellow, and I got the expected 0.85 through 4.2 Volts output (depending on position of throttle) from its green wire.

I would say that chances are very high that the yellow wire on your throttle is ground. To absolutely 100% confirm this would require testing the throttle as described above though.