The most important thing to know prior to installing any Pre-Wired Harness is the color codes for your pickups. You may need to consult your pickup winder to determine "Hot", "Series Link", and "Ground".
If applicable, "Series Link" wires should be soldered together and taped off.
Make appropriate solder "Hot" pickup connections to the toggle where indicated in the diagram above.
All "Ground" connections should be made to either of the potentiometer casings wherever most convenient. These connections include:
String / Bridge / Chassis Ground - this is the thicker single wire coming from the bridge/stop bar that grounds your stings and tuning machines
Pickup Signal Ground - This could be a braided shield on the outside of your "Hot" leads if using a vintage style pickup.
Pickup Chassis Ground - This could ALSO be the braided shield on the outside of a vintage style pickup. It can also the be bare wire in the 4-conductor lead.
Once these steps have been completed it's a great idea to plug in your guitar and conduct a "Tap Test" with screw driver on your pickup in all toggle positions.
If a sound is achieved you should be in good shape and are ready to mounting your pickguard to your guitar body. If not please do not hesitate to reach out, let me know what it's doing (or not doing), and pictures are always helpful in diagnosis any issues.