To control the MD, try switching in/out different resistances across pins 2 and 4:
pause: 5.15kOhm stop: 7.04 kOhm << 1.00 kOhm (also activates play) >> 3.62 kOhm vol inc. 9.88 kOhm vol dec. 8.39 kOhm track mark 11.88 kOhm