Can you supply a picture?
They may have left the thing in PA mode, check for the CB PA switch and see if that needs to get toggled the other way...then get a 4-pin Microphone wired for Uniden - Cobra - Galaxy 4 pin style...because you have to swap the wiring using the 4-pin plug to fit the 4-pin jack.
You REVERSE two pins on both sides (I know it sounds weird) but when you look at the plug, the wires are mirrored to the notch both sides stay apart in aspect, but the Audio Ground and RX and TX paring is reversed - easy to understand in some approaches.
See below - each pin has an assigned number you should be able to see it in strong light and a good magnifying glass to help. Notice the "notch" and follow the pin numbers.
1- Audio
2 - Ground
3 - TX
4 - RX
UNDER CONSTRUCTION
Here's why?
IT ain't right when it comes to NOTCH.
Because
if you follow PIN designations - it's above but the NOTCH is not correct in ASPECT to the wiring.
It could also be this...
Pin 2 to Pin 2 ASPECT - is ACTUALLY PIN 2 by Identifier LOCATION (GROUND COMMON)
However...
To Get Receive:
Pin 2 - SHORTS TO - Pin 3
To Get Transmit:
Pin 4 (On Mic Plug) - SHORTS TO - Pin 2 ON MIC PLUG
Hence the MIRROR aspect...
Proceed at your own risk - cannot be held responsible for errors suppled in both schematic - manufacturer and Identifier pinouts incorrectly identified
Take your pick
Both use SAME COLOR Scheme - but due to schematic pin for pin identification - you may have to experiment.
So, the Mic "
Audio wire" goes to Pin 1 - whatever color you have wired in the mic for the Element (it uses two, but one goes to shield internally at the switch in the handset - that is also known as GROUND and or COMMON - Mic element is a two-wire element, so it needs to complete a circuit - that means, one to ground the other to AUDIO Pin 1 on your plug.
You'll have a Braided wire or known as
SHIELD - that goes to Pin 2 GROUND / COMMON
Pin 3 is the contact that shorts to your Pin 2 when the mic is unkeyed (plunger out) That is
Receive
Pin 4 is the contact that shorts to Pin 2 when you key the Handset- push the plunger in, to Transmit