I have a Regency Polaris MT550XL scanning marine vhf set. It's an older
one, but still works good.

Problem is the mike is missing, for some reason. I have a spare, but will
need to put a replacement plug on it. I need a 5 pin twist lok plug for the
unit, and a way to figure out which wires in the mike go to which pins in
the plug.

Using the chassis socket, I can find a ground pin. That takes care of one
side of the mike element, and the PTT function. I can also power the set
and find which pin is 12v+. That leaves the mike element audio lead. How
do I ID that one (that only leaves three pins, so it's one of those)? Any
tattletale resistance to ground for the audio pin? I think the remaining
two pins are probably unused, after getting the three right for the mike
cord.

And yes, I'm trying to get a schematic. That would make it much easier.
I've searched around and don't find one yet. Sams Fotofact may have one.
I've asked them. Their search engine doesn't come up with one, though.

Where can I get a 5 pin twist lok mike plug? Don't know what the actual
name of such is, so may not be able to find because I won't be searching
under the right name for it.