You can get parts (including the wire harness) for your Coolster here;
https://coolster.com/vehicles/atv-3125f2/
The harness is on page 3.
https://coolster.com/product/wiring-...c-atv-wire-39/
Question though; Coolster shows the Mountopz as a 3125F2 but you say you have a 3125C. You'll need to know the correct model to to get the correct parts.