The assumption is that you have aquired a Motorola GM300 equipped with a 16 pin
accessory plug and that the radio is pre-programmed or capable of being reprogrammed
to the band of interest i.e. 2 meters.

The following images should be self explanatory in wiring the WB2REM ULI to a GM300 series radio.
These documents also address the low audio issues that may be an issue with these radios.