OMG Mode for Jazz Bass

It's not a resistor, it's capacitors:


The top left of the schematic is where you want to look.

G&L Wiring Diagrams and Schematics

Here's the associated wiring diagram:

 

You should use a .1 uF capacitor for OMG mode.

I can't see your attached diagram, @Brent's Groove, but assuming it's like this, you just need to replace the jumper with the capacitor. One caveat: the OMG circuit means your pickups won't be humbucking any more, so you'll hear some 60 Hz hum.

 

Cool, report back on how it works, I’ve been curious about this on a J bass!

if you don’t like it, another simple trick is to wire a cap in series with the bridge pickup to kill some of its low end... it’s supposed to sound fuller when blended with a neck pickup (less mid scoop).

I may just need to get a J bass and experiment

 

Use this diagram for Series/Bridge coil/Neck Coil with OMG mode if you so desire:

Just don’t mind the bottom switch. I used this with MM pickups successfully.


the other diagram posted by @fermata I never actually tested. I just traced out the wiring and drew that up...assuming....
So test it if that works before you hang me.

 

Yes, a la Rickenbacker. A .01 uF capacitor works well for this. But because it flips the polarity of the pickup, the two J pickups would no longer be humbucking, so it may be better with a PJ setup. The other side effect is that the bridge pickup will no longer work very well soloed, if that's a concern.

Also, it only works when the pickups are wired in parallel with each other, so it's not ideal for the OP's wiring, since it would cut bass on both pickups wired in series. Speaking of series wiring...

If one ends up preferring series to parallel or one doesn't like the volume change between series and parallel and is OK getting rid of the parallel mode option, @eastcoasteddie's diagram above is very clever.

I've used to good effect on two basses (using a .1 uF cap). Switch up is standard series wiring, and the other two positions (using an on-on-on switch) are two--count them, two!--OMG modes.

With a MM pickup, where the coils are very close together, the difference between the OMG modes is a shift in midrange emphasis. A series-wired Jazz bass has a humbucker with very widely-spaced coils, so I would anticipate a significant difference between neck pickup OMG and bridge pickup OMG, and they'll probably both sound cool.

 

And that’s exactly why I did this, because I simply cannot stand the volume drop between Parallel/SC and Series. A nice way to combat that is to add a Mini trim pot to the Series setting in order to dial it back to match output of the other modes. I have yet to try it, though.
So when I wire up MM pickups, I usually prefer Bridge Coil/Parallel/Neck Coil as I did with my latest project. But if I go with Series wiring, I would use OMG on both SC modes for balanced output.
The Jazz pickup spacing with OMG modes would definitely sound interesting, I am intrigued.
Also, I came up with that wiring purely by accident. I was wiring the bass up as per the first diagram (the one I never tested) and accidentally wired it up as the one I posted. I was shocked at what I did and never corrected it to the first diagram...which is why I never did test it...