Re: Rg670 wiring help
There is a number of things that could be the culprit.
What you explain is probably that the single coil is out of phase with the bridge pickup.
Since it works fine along with the neck pickup, I would assume that you should reverse the wiring on the bridge pickup. If your bridge pickup is wired with red as hot and green to ground, you could try to switch red with black and green with white (dimarzio colours).
Another thing that could be happening is that the magnet poles are out of phase. You have to make sure that the coils always have the opposite magnet pole.
I guess the Jem555 wiring diagram would be the right one for your guitar, but the heavy blues pickup is a 4 conductor single coil, which makes it a humbucker. To make this a single coil, you need to use black as hot, solder red and white together and isolate them, and green to ground. If that makes it phasing, switch green and black.
I have seen several times on jemsite that players don't do this, but the result is hum cancelling in position 2 & 4. If you keep the single coil with red as hot and green to ground your guitar will hum in position 2&4 and will be hum free in pos 3. Not my cup of tea.