I didn't get any help on my odd 2 wire IBM problem, (I couldn't figure it out either), IBM - Need help trouble shooting a 2 wire IBM / Simplex system. so I am going to try a work around. I am making a three wire to two wire converter. See drawing. The K1 relay is large and slower then the reversing relay and serves as a time delay so a pulse doesn't get out before the contacts can transfer. Any thoughts? Better circuit?