Building o2 simulator -- almost there!
 

Am going to build an o2 simulator to get rid of the pesky p0421 code. The following site has a great explanation but our Mazda wiring colors are different.

http://www.newcelica.org/forums/showthread.php?t=216641


Rear heated sensor on a 2000 626 2.0 colors are
LtGrn/ Black
Blk/Wht
Blk/Yel
Yel

Which wire is RECEIVING the reference signal (about 450 Mv) from the ECU and which wire is sending the signal back to the ECU.