96 7.4 Vortec MAF wiring questions

[ImNoSpaz]

I'm running the 96 7.4 Vortec in my 67 c10 and am at the point of doing the air intake system.
Hopefully someone can answer my question, and I apologize if this is the wrong forum.

The small wire harness for the MAF has two connectors. 1 goes to the MAF and the other went to the OEM plactic 90 degree tube between the MAF and the air filter box, and plugged into another small round sensor.

My questions
1) What does this small sensor do?
2) Is it necessary?
3) If necessary, does it belong before, or after the MAF sensor, or would it even matter?

I'm not using any of the the original tubing or airbox. Doing all new stuff from scratch.