Disclaimer: Open your radio at your own risk. I claim no responsibility for any damage caused or warranties voided.
I recently modified my Futaba 10C Radio (non-module version) to accept a Spektrum DSM module. Here is a video overview of the project...
The idea originally came from reading this page on connecting a Dragonlink module. I did not follow their instructions, However I did use their pin-out shown here...
Based upon this, I wired a 4 conductor audio jack into the transmitter. Since I wasn't able to thread the nut on, I used some J.B. Weld to secure the jack into place.
The wire colors are as follows...
Yellow: PPM
Red: +V
Purple: Ind
Black: Ground
Similarly inside the module, I connected another jack.
Here are the finished versions...
I accidentally cracked the enclosure for the module while drilling out the hole. I CA glued it back into place. It seems to be holding pretty well.
If you have any questions please comment below and I will try to fill in more details.