Here is what I had to do to get AFP working with my JR 378 radio:

Instead of using an adapter, I did a quick soldering job, which is more convienient that adding a longer adapter to the back of the radio (the plug position is on the lower back of the radio, which is already inconvienient for the standard plug.)

In case anyone else has the same issue, the soldering job was pretty easy:

- unscrew the black plastic plug cover from the back of the plug.

- under the cover, you will find three leads corresponding to the upper, middle, and lower (the tip) contacts.

- find the leads for the upper and middle contacts. solder a jumper between these two.

- replace cover and fly!