Batboard

Motorola is putting 12V across the speaker + & - lines on the accessory connector.

Discuss

Same thing as Spectra, GM300, M1225, ect. It is called a Bridge Amplifier as the speaker power amplifier so you will see about 6 volts from each speaker line to ground.

That IS why you do NOT want to ground any speaker leads.

Even portables have the same type of audio output stage.

OK, I'm an idiot. It would help to have the pins on the right lines when taking measurements. Turns out I had my pins on 7 & 8, not 9 & 10. 7 & 8 just happen to be B+ and Ground. A logical explanation for why I could not find the voltage today when I did some more snooping around. There is NO measurable DC across the speaker lines.

From some more in depth testing, the only thing I can really tell that's different between the TRBO and the 16 pin models is the TRBO max volume results in about 10VAC while a CDM at max volume results in about 9VAC on the speaker lines.

My ohm's law tells me that's not statistically significant

Much ado about nothing, nothing to see here, carry on etc etc

I can tell you that if you buy a radio from Bearcom that they have added a speaker jack to on the side of the chassis, and you mount it in a rack and accidentally ground the speaker jack, you can get a nice burn scar on your hand when you reach into the back of the rack when the radio has been running for a while, it gets damn hot. Needless to say, that over sight was eliminated.