RA-25K DB9 Pinout:

1 = TX Audio

2 = Not Used - (hardware COS input (AllStar) when JU1 is installed)

3 = PTT

4 = Not Used - (hardware CTCSS input (AllStar) when JU2 is installed)

5 = RX Audio

6 = Ground

7 = Not Used - (Goes to available hole "7")

8 = Not Used - (aux TX audio when JU3 is installed)

9 = Ground 

Some folks have remarked about the partially illuminated PTT LED when 
the radio adapter is connected to a radio that has a PTT switching voltage
 (bias) of less than 5 volts.  This situation causes the red PTT LED to 
partially illuminate.  This partial illumination can also happen with just 
about any radio when the radio's power is turned off - falsely making it 
look like the radio is transmitting.  A BAT43 Schottky diode has been added 
to the RA-25K that eliminates the false illumination from happening.  

Jumper (J4) has been added to disable this diode option and restore the 
PTT circuitry to original if the diode should create a problem for a 
particular installation.  The jumper simply shorts out the diode.

Additionally, several items like the hardware COS and CTCSS inputs 
(used for AllStar Link) and the second audio output are not needed for 
VARA FM or other digital modes. In fact, if something is connected to 
the COS and CTCSS (Volume UP and DOWN pins) bad things can happen with 
Windows based programs.  In addition, DCD (XDC) and/or other logic or 
control lines might be connected in existing installations using the 
KPC-3 or similar TNC.  These functions affect pins 2, 4, and 8 on 
the reconfigured DB9. These DB9 pins can be disabled by the absence of 
the  "JU" jumpers at locations JU1 thru JU3.  As such, even if these 
pins are tied back to the radio somehow, it won't matter - their 
existence won't affect the operation of the RA-25K for this application.
  These jumpers could be installed into these locations if there's ever 
a need for them; restoring the RA-25K to the same capability - 
functionality as a RA-25, except for the different DB9 pinout. Plus, 
these hardware inputs may be implemented sometime in software  - 
permitting DCD or some other digital feature, so I don't want to 
limit the hardware from using them in the future. 

By default, we recommend NOT installing the short on JU1 thru JU4 
for VARA FM or other digital mode usage.