[ba] mac 11 mystery wires?

[Brian Devlin]

Near the end of http://www.sjmautotechnik.com/hpgraph.html#s2,
SJMautotechnik says "The Hitachi "MAC-11" Engine Control Unit used
with the "MC" engine has two timing maps, one for Premium and one for
Regular fuel."
Is this choice made by the various ground wires that may-or-may-not
be present at the ECU, or the knock sensor, or gas sniffing elves in
the fuel distributor or what?
Send this along to the main list if you like, I'm only on the Bay
Area and Torsen lists.
-Brian