3Bpin37 is flyback (EC36pin23). Injectors are powered from the ECU via this pin (see MembersPage/PeterJensen/AudiSwiring, 3B is different from the AAN/ABY/ADU in this respect).

3B ECU internal relay (standard, unless requested otherwise):

Relay coil powered from:

* mot55/27 +12V when ignition is ON (EC36/25 ECU supply pin)

* GND

Relay output switch "normally open" (closed when ignition is ON = ECU is powered up)

* 3B MOT55/pin18 (VBATT constant +12V, even alive when ignition is off)

* 3B MOT55/pin37 (EC36pin23). Injectors of the 3B harness are supplied from the ECU via this pin.

The idea is NOT to draw much (2A+) current from 3Bpin27 because we fear that might damage the ignition switch.