EGO/HEGO wiring.

[xxalexx at ix.netcom.com]

> >usually the heater wires same color white(or was that black)
> >and sensor grey?
> >I have not seen any other colors except solid  blk, white,. grey
> >and  I'm not color blind.
> >Wiring diagrams sometimes have the colors before there own connector
> >changes colors.
> >alex 
> 
> My NGK Ford three wire units are two white (heater) and one black.
> 
> The Four wire adds a gray wire. I assume it is the sensor return but have not 
> tested it yet to make sure they didn't make the black the return.
> 
> Charlie

It seems Bosch and GM use same colors.
I check heater for ohms (which not much)
Check O2 wire by putting in exhaust an measure voltage.
Note I have never seen any huge ground loops in sensor 
and have used 3 wire in place of 4 wire in some applications with insignificate 
changes in federal emissions.  I think I recall some early Bosch schematics
were the 4th wire is just used as shield.   
alex