The solenoid is normally closed, but when you apply 12 volts, it opens the ground path allowing the engine to run. Once the 12 volts is removed the solenoid closes to ground shutting off the magneto's power. One per magneto is required.

PN 8134 can also be used in conjunction with a master cut off switch to "kill" the magneto - MSD or Mallory.
The solenoid is normally closed, but when you apply 12 volts, it opens the ground path allowing the engine to run. Once the 12 volts is removed the solenoid closes to ground shutting off the magneto's power. One per magneto is required.

PN 8134 can also be used in conjunction with a master cut off switch to "kill" the magneto - MSD or Mallory.