This is my first thread and I couldn't find anything on it.
I own both a gibson MIII (or M3) and an Epiphone EM-2
These have a special wiring for their HSH pup.
There is a little two position switch and lower position have 3 last position of the 5 way switch act as les paul switch (Neck/both/Bridge). the upper position of the swict gives a standard strat 5 way switch. That means split neck/split neck plus middle single/middle single/split bridge plus middle single/split bridge.
I want to change the pup of these guitars for better suited ones. The MIII I bought loaded with an unintesresting Carvin neck pup and a Ducan full shred (not exactly my taste) while the EM-2 has stock low value humbuckers...
Problem is I don't undersantd a single thing as how this wiring works.. So changing pup from a brand to another will be risky...
I've never seen one of these type of guitars, so I can't help you understand the wiring of the switches. But you don't really need to understand the switching since you want to leave the switching "as is" and just change the pickups. You're not really going to be rewiring the switch.
You simply need to trace the wires from your three pickups, make a diagram of where those wires go, and wire the new pickups to the same spots, Each of your humbuckers will have 4 wires, plus a metal shield wire which will always go to ground. Your single coil has 2 wires. At least one wire from each pup will go to ground, so you really probably have no more than 7 wires to wire to the switches. Not so bad. eh?
However, be aware than different pickup manufacturers use different color schemes for their wires, so if your new pickups are from a different maker than the old, you need to make a chart corresponding the old colors to the new. There are charts of common pickup wire colors to help with this, there is one on this board in the reference section- I tried to link to it here but the link won't work.