Before beginning, note that if your Jazzmaster has existing ground wires, do not remove them. These are essential for the shielding. As the Jazzmaster is known for being a noisy guitar, you must connect these wires to your new harness to ensure the electronics are properly shielded.

It is crucial to install the phase switch in the correct direction; otherwise, the controls will operate in reverse. Ensure that the cloth wires are facing down.

Begin by installing the Neck pickup. For this specific pickup, the white wire is the 'hot' connection, and the black wire is the ground. Important Note: Pickup wire color coding can vary by manufacturer. Always consult your pickup's documentation to correctly identify the hot and ground wires for each pickup.

Solder the Neck pickups Hot to the middle right lug on the phase switch.

Solder the Neck pickups Ground to the middle left lug on the phase switch.

Solder the Bridge pickups Hot to the middle lug on the Bridge Volume.

Solder the Bridge pickups Ground to the casing of the pot.

Next, solder the earthing grounds (mentioned previously) to the casing of any available pot. For this specific installation, the casing of the Neck volume pot was the most accessible choice.

Carefully reinstall the pickguard. Take your time with this step, as frustration here can easily lead to problems. The most common issue is improperly balancing all the wires and controls within the cavity. To avoid killing the signal, ensure no wires are compressed and that none of the pots or the output jack are pressing against the cavity walls.

After positioning the pickguard, secure it by installing one screw in each of the four corners.

Before fully installing the remaining screws and the strings, you must test your work. Plug the guitar in and use a metal object, such as a screwdriver, to lightly tap the pickups. As you do this, cycle through the main controls (Volumes, toggle switch, and phase switch). If the wiring is correct, you should hear the tapping sound through all these main controls. Just note that you will notice a sonic difference when testing the standard tone control, but not when testing the bass contour.