bsooley,
the Book by Adrian Streather on the 964 probably has the codes deciphered. There is a publication on OBD1 codes "Bosch F.I. System, OBD codes" out there but I don't have the exact reference. Post query on rennlist and they should have a source of the codes. The correct adapter plug for the 964 OBD1 connection to the Bosch Hammer is unfortunately not readily available. I believe a mercedes plug also works but don't know which model mercedes benz. I have had luck with getting OBD2 cables from
www.carplugs.com, contact them for leads to OBD1 connectors (worth a shot, good luck).