The cable is used to hook up a milliamp meter in series with the EHA. You measure current in milli-amps, not voltage. Should be 0 mA at idle with the mixture set correctly -- set it with the 3mm screw fitting in the fuel distributor.

Peter

Ah yes, the old, i got in a hurry and forgot trick. I was using voltage settings, I was in a hurry to use my new test harness tool thingy this afternoon and only had about half an hour. Ya, I remember now and I can do the test in mA. I just forgot, or I got in too big of a hurry more like it.
It should be at 0 mA at idle with the engine warmed up and the o2 sensor warmed up and working correctly ( signal fluctuating back and forth ) Right?