- 1). Drill a hole under the dash to mount the switch. Start with a smaller pilot hole and work your way up to the size needed. The final diameter should be equal to, or slightly larger than, the shaft of the switch. Make sure the drill bit will not touch any wires under the dashboard.
- 2). Connect one end of the in-line fuse holder to a hot terminal on the car's fuse panel. Connect the other end of the fuse holder to one terminal of the toggle switch. If the wire is not long enough to reach the switch, add an additional length of wire and connect it to the fuse holder wire with a crimped in-line connector.
- 3). Connect a wire from the device you want to control to the remaining terminal on the switch. Connect the other wire on the device to a ground on the vehicle. When the switch is activated, the device will have power.
- 4). Push the switch through the hole you drilled earlier. Use the nuts and washers supplied to secure it to the dashboard. Tighten the nuts with pliers.
- 5). Tuck loose wires under the dash and secure with tie-wraps.
Put the fuse into the fuse holder and flip the switch to test the circuit.
Source...