Even though this controller has a 5 wire throttle connector, a 3 wire throttle can be used with it by only using the controller's throttle connector gray, green, and red wires, and not using its black and orange wires. For a small fee ($5.00) we could custom make a plug-and-play adapter that would convert the SPD-36750A controller's 5 wire throttle connector to be a 3 wire throttle connector. We would just need to see a photo or drawing of the existing 3 wire throttle connector in order to do this.
Please let me know if you have any questions, or if you would like a 5 wire to 3 wire throttle adapter made for the SPD-36750A controller.
We have a kit that includes a THR-500 throttle and SPD-36750A controller for $94.95. Here is a link to it: https://cart.electricscooterparts.com/ProductDetails.asp?ProductCode=SPD-36750A-THROTTLE-KIT