Just what, when and where is this O2 monitor lamp the factory manuals speak of in diagnostics 2-7 p44 of XT at least? Is this the red LED of the ECU itself not a dash light?

It is the LED on the ECU.

ON is rich or lean,dont remember which.

 

there is a hole in the case of the ecu about half way down the side and if you look inside you can see s a green LED flashing.  It also displays the codes in diagnosis mode