I am trying to restore an Ibanez RBM2 with EMG pickups and I am having an issue. This guitar is equipped with 89/SA/SA. The 89 is split on a push-pull, no tone knob and there is an EMG SPC circuit that is supposed to be wired to a dpdt toggle switch. Currently everything is hooked up except the SPC, nothing is connected to the dpdt switch. I am looking for a diagram to hookup the SPC.
I assume that you've tried the Ibanez support website, only to find that their diagrams begin in 1994- and your RBG II is a 1991. Anyway, that's what I found when I looked for a diagram. . .
As I understand it, the SPC is a "mid-boost" circuit. It may be that you can find a diagram of another guitar which uses that piece and adapt from that diagram to yours. Short of that, we can do some educated guesswork.
First since this is an active circuit, it has to be powered, and the usual way of doing this is to have the 9V wired to a TRS (i.e., stereo) output jack so that the battery is disconnected when the guitar cord is unplugged. I'm guessing that this shares a 9V battery with the EMG pickups? Can you verify whether the SPC looks to have been connected to the jack at some point?
Also, how many wiring "pads" (or contacts) does the SPC have? Are they labeled at all?
The DPDT switch is undoubtedly for "SPC ON" vs. "SPC bypass". This implies that you would have 4 leads coming from the SPC- a signal in, a signal out, a 9V + power lead and a 9V- ground.
The 9V probably gets wired to the output jack, as discussed above, and the other end goes to ground (or to power, depending on whether the - or the + is connected to the jack). The DPDT switch probably takes the output from the pickup switch to one of the center terminals, the other center terminal goes to the Volume pot. the top lugs of the switch go to the signal in and signal out of the SPC, and the bottom two lugs are wired together for the bypass, when the switch is in the other position.
One question I have is whether the SPC is wired before or after the Vol and Tone controls. Given that the EMGs are active pickups, I'm guessing "before", but I could be wrong on that.
Probably your best bet is if you can take some well-focused close-up photos of the SPC and your existing wiring, we can probably suss this out from there.