In addition to the voltages I sent a day or so ago that I took with the MAX converter in place, I disconnected the RS232 from the MAX and took measurements directly from the female end of the RS232 connector. The only significant voltage I found was +5V between pins 5 and 9. I then checked the DC voltage between Pin 5 and 3. When I pressed the 'Horn" button on the controller the reading went from 0.0 to 70mv while the horn was depressed.
Hi David -
If you have a Legacy base, the voltage between pins 5 and 3 should be about -7.5 VDC (I just checked on mine). (True RS232 signaling holds the TX line at a negative voltage when idle.)
I am not sure where to go from here... there could be an issue with the cable you are using to connect to the Legacy base, as I mentioned above.
Do you have the Legacy Y-cable that came with your command base, or a SER2 module? You could try the serial connector on one of those, but you ought to be able to read commands at least direct from the base,