Strange Collant Sensor Connections

I was checking the circuit for the coolant sensor on my 78 280Z, and it didn't check out right:

One connector from the sensor goes to the ECU, pin 13, like it should. The other one goes to ground. The circuit diagram shows the second wire going to ground, but when I plug in the coolant sensor with the engine running, the engine stalls, and then won't start again.

I checked the circuits according to the EFI 'bible', and the coolant sensor seemed to check out fine. But still the engine won't run with the sensor plugged in

So I have the coolant sensor unplugged, and the engine runs extra rich (about 10 MPG).

Any thoughts on what might be happening? I put in a new sensor over the winter. My next move would be to take the car to the dealer, and I bet the 'expert techie' will look at the hood and say, " You need a new AFM" ($600!!)

thx