P-Bass Pickups
Grounding
A very important note here is to ground the bridge. If the bridge is not grounded your bass will almost always hum when you are not touching the strings. If you still have hum problems you should also have or install brass plates under the pickups, and have them connected to the common ground, usually on the back side of the volume and tone pots. Make sure that these plates do not short out the pickups. You can insulate these plates with electrical tape or some other insulator.
Split Coil
P-Bass pickups are split coil type of pickup. The two coils are wired in series, in most cases. However, you can wire them in parallel too, which will make the sound brighter, with less bass. The recommended wiring practice is to wire them in series so that the coils are out-of-phase with each other. This practice causes the pickup to become a hum-bucking (hum-canceling) pickup coil. The advantage in this practice, is to make it immune to outside electrical noise, which is a great plus for any bass. Of course, you can change the pickup wiring to single coil with these, by switching the wiring on one of the coils. Usually, the coils come with color coded wire connected to the coil terminals. Some coils use Red and Black, while others use White and Black.
Electrical
Notice that the split coils are actually out of phase here. It does not matter in this case that the coils are out-of-phase, since there are no other pickups here. If the coils are wired in-phase, then it becomes a single coil type of wiring, and you can expect to hear hum when your are near electrical fields. The Precision Bass pickup is what is called a split coil type. The purpose here is to reduce external noise (i.e. hum from stage lights, radio stations, lightning, etc.) to the sensor and only produce the sound of the strings.
Wiring Help for P-Bass Pickups
