In the case of Chance PI, I have 2 pins to the coil, obviously TX & RX. Bought another coil from aliexpress a concentric coil, 5 pin, I have continuity pins 1&2 & pins 4&5, pin3 no register. mono wiring above, short across 1&5 get reading of 027 at pin2, reading of 011/010 at pin4 nothing pin3...