You have a math problem. Five doesn't equal four. If you have only four wires this presents you with three choices. The 5-pin mike socket has two ground pins, number 2 used for mike audio only, and pin 4 used for transmit/receive switching only.
You can hook your single ground wire to pin 2 and choose feedback noises in SSB receive, hook to pin 4 alone and choose feedback squeal in transmit, or tie pin 2 to pin 4, hook the shield to that and maybe get both.
Some folks get away with this and have no problems. Other folks will experience the feedback issues I mentioned. Hard to predict which radios will or won't misbehave this way.
The mike cord can be analyzed first by which wire has the shield wrapped around it. This is the audio wire and goes to pin 1. A continuity test from shield to each of the other two wires will reveal the receive wire that goes to pin 3. And the wire that shows continuity to ground when keyed goes to pin 5.
And how you hook the shield to pin 2, or pin 4, or to both is up to you.
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