I assume that drive 0 was DS3 and drive 1 was DS4? Please confirm.

I managed to make up the required circuits and LEDs for a BA23 box with 2 hard drives and an RX50 (placed outside of the BA23, but connected with long cables to the normal connectors) connected to an RQDX2 via the standard distribution board adjacent to the hard drive bays. I remember that lines 3 and line 4 on the 10 pin cable supported the second hard drive. My first attempt jumpered line 1 and line 3 along with line 2 and line 4 to allow the 4 button panel to support both hard drives as long as they were BOTH in WRITE PROTECT at the same time. The circuit I developed much later needed two switches, two resistors and 4 LEDs.

On occasion when I need two hard drives in an BA23, I disconnect the 10 pin cable to the normal 4 button panel and connect that 10 pin cable to my contraption.

I am curious, do you have the circuit needed to support the second hard drive? And did you have to cut any traces on the 4 button panel? What I don't understand is why DEC did not make the information easily available if you found it so easy to make supporting a second hard drive possible. But back then, I guess DEC was DEC. It was much more profitable selling an expansion BA23 box or better yet a BA123 box.

Jerome Fine