Very brief outline, if you think of 4 wires where A & B are the start and end of one coil and C & D are the start and end of the other
Series is both coils but the end of one is the start of the other. So it is A to live, B & D connect and C goes to ground (the circuit through each coil is in the opposite direction).
Parallel is A and D to live, B and C to ground. Still humbucking, coils still go in the opposite direction. It is the same connection as Fender make when they hace 2 pickups on at the same time in a Strat or Tele.
When I wired Ben's Agile, I was pleasantly surprised at the quality of the pots and switches in it. So much so that I used one of the original pots and the original PU selector as the tone switch. The only thing other than the pickups that I changed was to replace most of the connecting wire with good quality screened wire.
The other mini toggle that replaced a pot is the pickup selector.