Where to connect AFR sensor?

For now I connected it to the seat belt starter interlock. The male end of that connector is removed, but the female end is still dangling on the fender with a connection to J2 and another connection to what seems to be a common ground shared by the lights (I think the circuit diagram said S9). All I had to do was crimp spade connectors onto the AFR gauge wires and plug them into the empty sockets in the starter interlock connector. The sensor seems to work like that. I've ordered a Bosch relay and will do that project when it arrives.