I'm have a number of GM339 series mobile radio's hooked up to record the filtered audio at a flat level that is not changed via the speaker volume so I'm using pin 11 (rx filtered audio) and pin 7 for ground.

I need to to the same with some XTL2500's and understand pin 21 on the rear connector is the filtered audio however there appears to be two ground pins, 1 and 14. I cannot seem to tell if there is a difference or if it matters which one I use.

Anyone able to advise?