Some interesting differences
 

So i bought an 87 rx7 N/A s4 "The greatest day in my life almost". The motor(A) was seized, so I drained the oil it was white! So i bought another motor(b) for it with the impression it was the same s4 N/A motor. While checking the new motor out i found that the banjo bolt for the oil cooler lines on the rear housing was not there. Instead it had one like the fitting on the front Housing. No big deal just swap in the old one call it good. Then i noticed the Oil pan on the original motor had a second fitting other than the Oil level sensor. Maybe a temp sensor? Now is it possible that the guy i bought the motor(B) off of swapped in an older oil pan? I wonder what else i will find if i go any deeper.

Tell me about it. Almost same thing happened to me when i swapped engines from a broken european 12a 83`to a usa 12a 83`. There were many differences whitch i didnt see until the new engine was in the car. Real head-ache.

There are some engines that did have 2 sensors located in the oil pan.
The funny thing is you go to look up that sensor and Mazda Parts Catalog doesn't even show it exists.
You would be fine to hook up the sensor that you need and just leave the other one unconnected.

That was where I looked first... I did however find out what it is and why it's there. It's a temperature sensor for the cold start assist. So it is worthless, but I can now use that spot for a real temp sensor:). Have yet to dig any further because I'm moving and I just need the car in a transportable state. When I get settled in we will see what else is buggered on the motor.....