Wiring 2 P90's in a 1972 SG-200=Hummmmm

[theundeadelvis]

Hey guys! My buddy asked me to drop a couple Lollar P90's in his 1972 SG-200. I wired it up and it hums something awful. I've installed new pots, the pickup wires are shielded. The SG-200 uses to slider switches to turn the pickups on and off. Originally it had 2 single coils in it. Here's the wiring diagram I am using (I have the shields soldered as the brown wires and the inner wire as the black wires):

When both pickups are on it's pretty quiet. But using either the neck or bridge pickup alone results is bad hum. I do have the bridge grounded to the jack. Any suggestions on what may be causing this?

Thanks in advance!

[Shrapnel]

Hey guys! My buddy asked me to drop a couple Lollar P90's in his 1972 SG-200. I wired it up and it hums something awful. I've installed new pots, the pickup wires are shielded. The SG-200 uses to slider switches to turn the pickups on and off. Originally it had 2 single coils in it.

When both pickups are on it's pretty quiet. But using either the neck or bridge pickup alone results is bad hum. I do have the bridge grounded to the jack. Any suggestions on what may be causing this?

Thanks in advance!

Have you tried to contact Lollar? I know in his videos on Youtube, he's fanatical about any wire over 1" in length being shielded., it might be worth the effort to see if you can get his opinionl. Or try this question over at http://everythingsg.com/forum/

[HotBluePlates]

I'm assuming their is a connection not shown from the switch grounds to the pot and jack grounds. Is that the case?

P-90's are gonna hum to some degree, because they are single coils. They are also *strong* single coils, so they will likely hum more than a Fender pickup. Some Gibson models have dummy coils situated below the P90 to reject the hum without adding output level or changing the sound.

Are you sure there is not an issue with proximity to a monitor, flourescent lighting or a power transformer? The pickup will readily catch that noise.

[theundeadelvis]

Thanks guys! There's no other wire. The switch ground point is a tab on the rivet that mounts it to the control plate. I found that wiring diagram, and I believe that's how it was wired when I took it apart (I lost my drawing at some point). I may try contacting Lollar like suggested. Thanks for the suggestions!

[HotBluePlates]

There's no other wire. The switch ground point is a tab on the rivet that mounts it to the control plate.

Is the control plate metal? If it is, did you measure continuity between the pickup ground wires and the jack ground?

There should be some kind of connection between the pickup grounds at the switch, the pot grounds and the jack ground, including the string ground you mention.

And I'm not sure, but your diagram looks like it selects either pickup by itself or both in series. Is that what you intended?