Classic HP forums?? - plotter questions

I got no bites the first time, so I'm trying again. Does anyone know of any good classic HP forums, sites, or parts sources? I need to construct an interface cable for my recently acquired HP7202A flatbed pen plotter. This plotter was manufactured around 1971 and could be interfaced using one of three styles of interface cables (it appears that they all plugged into the same male adapter port on the back of the unit, but must have used different pins). I plan to use the 20mA style of hookup, which I assume will use four of the pins. I just need to determine which of the pins are used for the 20mA send and receive. Other options were for an EIA (RS232) connection, and a third type of connection. The plotter is controlled using ASCII commands to plot points or lines. I am looking for someone who may have had some experience with these plotters in the past. Even better (although not likely) would be that someone would have an interface cable. These are HP part numbers 17251A, 17252A, and 17253A. Last night I repaired the fuse housing, cleaned out the dust, and powered on the plotter. It worked fine in standalone mode. The electrostatic "chart hold" feature held a piece of paper in place on the bed, and the lower left and upper right "pen set" functions worked, as did the "pen up / pen down" button and the controls to move the pen. The plan is to hook this ancient device up to my 11/40 as part of my classic computer center. Ashley Carder http://www.woffordwitch.com