Yes, High - means RX mode - LOW - means TX - Low = Grounded.
So, if it floats - row with it.
Because the Service Manual shows 5-pin, but two pins are grounded - per schematic - but one is tied to the other - where? I believe the Mic socket - but this doesn't mean anything to anyone unless photos - for even the Service Manual cannot show this properly.
This is the HANDSET side (Plug)
Note - PIN 4 is not used
So, the Mic itself also needs to have 4-wire - but you really should short the same two pins - the socket would have to use for that SAME ground. That would be Pin 3 and Pin 4. In the Above graphic - they use PIN 3 on the PLUG side.
The Service manual isn't as clear on this - but to help....
The "MIC Audio" line heads to two spots. One to the main PC board, thru a RF Choke (RF201) 22uH - which is the LIVE wire itself - which feeds into a Limiter - Q106 - a PNP. It's tapped to the Collector, and also uses a Clipper D109 to help process the Audio so the limiter circuit sees positive going energy that can otherwise cause distortion.
The "other half" of these two wires is; what is interesting. It takes the AUDIO from the Receive Detect, up to it.
Why? Because of the way THAT wire is used.
Firstly 1 wire off of PIN 1 of the JACK side comes from the MIC AUDIO PLUG - PIN 1 - and routes directly to the main PCB. RF201 Choke
The 2nd wire heads up to the PA./SQ pot - which is used as a COMBINATION switch.
When the Radio is in RX mode, you power it up, ON/Volume - but you also have to make sure the PA/SQ control is not on PA mode. Anything above fully CCW is "PA OFF" - turning the PA/SQ knob fully CCW turns on PA.
The switch is a lot like the ordinary ON-VOL switch from other radio sets - but they use the switch contact side as the DPDT side that when NOT in PA mode - sends MIC audio to the RF201 Choke, and VOLUME knob then has RX on itself. SQ operates normally.
To keep the radio quieter, they route VOLUME thru R102 a 22K resistor - IN RX mode (PA off)
In PA mode - the RX VOLUME line is "Broken" - it's shifted from R102 - to RFC201 - raising the volume up - SQ is disabled so the person can control RX and MIC volume at the same knob. And you use the PA speaker jack for you to hear both RX and PA mode.
So schematically...
I'm just not sure how much help do you need?
Since
@TM86 was working with you - I only wanted to inject a "yes" to help you and if you needed verification - the Service manual and all its data - schematic and drawings on where things go - is the only way to help you both in finding a common ground - here, on the forums - to do it.
We're here...
If You Need More Help...
Then we'd all jump in and have that sucker Cobra'd into a Cadillac - all pinstriped - plated in gold and decked out in rag-top - as a chick magnet convertible ready to roll...