Power (bus 30) goes to the central connection of the contact switch.
When the key is turned to start it contacts the outer contact which brings the 12v to Relay 5 pin 86, and powers the relay coil.
Starter Relay 5 pin 85:
Automatic transmission: The other side of the relay coil is connected to the ignition interlock switch so that it connects to Gnd when transmission is in P or N position.
Manual: a jumper connects it permanently to gnd.
There is also a connection from pin 85 to the LH2.3 pin #30.
- when pin 85 of the relay (and this #30 of the LH) is connected to gnd, the LH knows it is in P or N position
- when pin 85 of the relay (and this #30 of the LH) is NOT connected to gnd (I think the LH pulls up the signal), the LH knows it is in R,D,3 or 2 position and idle speeds needs to be reduced.