Electrical Diagnostic Specs

[pp6000v2]

I have an HK radio that is giving me trouble in adding the hands free phone module (they can't hear me, but I can hear the caller audio). I have the EDM to troubleshoot, but I'm running into a curious case. The flowchart for troubleshooting wants to check for continuity on the 35 pin ultra connector [28B] as well as the actual radio [28A], between pins 22 and 33. I do have continuity on the radio, with no continuity/shorts on the harness side.

The flowchart recommended service is "replace radio." My confusion then is this: the pins 33 and 22 are MIC SUM OUT +/-. The CB radio will transmit fine, others can hear me normally. The HFM is getting some audio to it because, while quiet, callers can somewhat hear me. The diag manual also checks for voltage between pin 33 (MIC SUM OUT +) and ground, checking if it is greater than 9V. I get 4.00V just about every time, and a couple times got 5.38V.

What should the voltage measurement range be? And should there ever be continuity on the radio's 35-pin connector [28A] pins #22 and 33?