Volks, I repeat: I need the list's help to help me continue analyze the
circuit. As a bare minimum, I need:

>8. Now I need the list's help: I need voltage measurements from a known
>good ISCU unit, to try and find where the problem hides. It's not very
>difficult - all you need to do is connect a low power 12V source (wal-wart
>seems safer than 12V from a big battery) to pins 15 & 31 as described
>above, and tell me what you measure at all the other output pins. Also, I
>need you to connect a low-power test light across the outputs (St1 and
>St2) and tell me if it lights or not (it should IMO) or even a small
>loudspeaker to know if it's a variable signal.
>** be very careful not to short any adjacent pins so as not to cause
>damage **

This will also enable me to know I can continue analyzing on the bench
(without the engine RPM signal) and not inside the van which is much less
convenient.
Any takers?...