The EHA is on the right (viewing from driver's side fender) side of the airflow meter, underneath the airfilter that needs removed.

Plug your mulitemeter into the disgnostic socket (round,black, ~1.5 inches in diameter-screw off cap).

Set multimeter to duty cycle freq.

Red lead into hole3, black into hole 2-that is your ground.

Key on engine off (last position before starter engages) you should read a number.

Start car, you should read another number.

After the car warms up, and if you HAVE an O2 sensor, the numbers should change, and begin to fluctuate.

You do NOT need to touch the EHA for the procedure described above.

However, EHA current (which is also a representation of mixture) can be measured, and this is most easily accomplished with the MB EHA test harness. If you simply want to check mixture, either method will suffice, and the data supplied is equally useful.

PS- you didn't mention what MODEL and year your car is. Sure hope its a KE3 car, or this is going in the wrong direction!

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E