EMG P style pickup help magnets? Polarity?

That is how P pickups cancel hum- the two coils have opposite magnet polarity and opposite winding polarity/phase. This puts the two coils’ signals in phase, but puts the EMI hum picked up from the two pickups out of phase and thus cancelled out. You should find the same magnet situation to occur on all traditional P pickups (interestingly a Fender Mustang pickup uses two identical coils simply wired out of phase in order to cancel hum, so a bit different than a P though they look similar)

 

If you're talking about comparing the two magnets within one pickup and finding that they're opposite polarity, then @sunbeast explained it.

If you're talking about comparing the "top" magnet in the bridge pickup to the "top" magnet in the neck pickup, then it's not actually important. As long as both pickups are hum cancelling with themselves (i.e. the two coils in the single pickup are reverse polarity and reverse wound), and the two pickups are in phase with each other, the pair of pickups will be hum cancelling and will sound good. You don't technically need a given coil in the bridge pickup to be RWRP from the same coil in the neck pickup.

EMG (and many other manufacturers) do happen to configure P style humbucking pickups with RWRP for the two coils on the same position, mostly out of convention as a hold over from single coil pickups being RWRP from each other. As a bonus, a pair of such pickups will stick together face to face, just like RWRP single coils will.

 

I've just received a Fender Mustang Performer bass that the previous owner replaced the J pickup with a hum cancelling Suhr J pickup. This is great! However, whenever the split coil is engaged there is a hum. Is there a drop in hum canceling split coil pickup for Mustang basses?

 

Not sure why you put this question in this unrelated thread, but since I know what’s going on….

In fact most Mustang pickups are humcanceling- the Fender Performer bass might be the one exception because of the added J pickup.

You see in a P pickup you get humcancelling by both reversed magnet polarity AND reversed phase between the two coils, while the traditional Mustang pickup uses two identical coils (same magnet polarity) and they just reversed the phase to cancel the hum (since there is no shared bass signal but just shared noise signal between the coils they are still humcancelling without messing up the tone despite the strings then being out of phase with each-other). The Mustang scheme is humcancelling, but puts two of the strings out of phase with the other two so if you add a second pickup and try to blend the two pickups then you’ll find two of the strings will sound exceptionally thin when the pickups are blended.

The way Fender decided to make that work on the Performer Mustang was to just wire the Mustang pickup in-phase with itself (which also eliminates the humcancelling effects and essentially just makes it work like a single coil). You can reverse the phase of one of the coils of your current pickup to make the pickup humcancelling, but then it won’t mix well with your Suhr pickup. To get a Mustang pickup that is humcancelling AND plays well with other pickups you need to find one built like a typical P pickup (coils have reversed magnet polarity).

You might reach out to someone that does custom winds for pickups and who also makes Mustang replacement pickups who could build one for you, maybe Novak, Lollar, Nordstrand, etc.