As Hurshi states, the end result of all the sensors inputs is the voltage at the EHA. If you have no voltage at the EHA, your OVP relay is probably toast or a sensor is way out of line. For a correctly adjusted system, the voltage should be around 0 ma. From my understanding, the older systems adjust only positive ma, whereas the newer cars 1986+(?) adjusted either side of 0 ma (ie -10 ma to +10ma).