Re: Crackling / popping when i touch metal parts
It looks like the big black wire coming from the jack is an insulating cover on a grounded wire similar to the pickup wires. Make sure the metal braided part is grounded on the lug on the metal plate, and the inner wire is connected to the yellow wire (this appears to be the lead wire from the selector switch). And make sure that this wire is NOT touching any ground.
If the backs of all the pots have continuity with the plate when tested with your ohmmeter, and the grounding lug also has continuity (except for the lead wire from the jack, of course), then all appears ok.
If you still get a crackle when you rub a finger on the pickguard, then this is static electricity which is rare on a LP. The only way to completely get rid of that is to glue some foil to the back of the pickguard, solder a wire to it and run it under the bridge PU mounting ring (cut a small notch in the bottom of the ring, don't worry, it won't show), and into the body cavity where it can be soldered to a pot.
I don't see how what you describe can be related to the caps.
Make sure the P-Rails is grounded.
It looks like the big black wire coming from the jack is an insulating cover on a grounded wire similar to the pickup wires. Make sure the metal braided part is grounded on the lug on the metal plate, and the inner wire is connected to the yellow wire (this appears to be the lead wire from the selector switch). And make sure that this wire is NOT touching any ground.
If the backs of all the pots have continuity with the plate when tested with your ohmmeter, and the grounding lug also has continuity (except for the lead wire from the jack, of course), then all appears ok.
If you still get a crackle when you rub a finger on the pickguard, then this is static electricity which is rare on a LP. The only way to completely get rid of that is to glue some foil to the back of the pickguard, solder a wire to it and run it under the bridge PU mounting ring (cut a small notch in the bottom of the ring, don't worry, it won't show), and into the body cavity where it can be soldered to a pot.
I don't see how what you describe can be related to the caps.
Make sure the P-Rails is grounded.