OK, point by point, inline responses. I'm making the assumption you want to set up a standard Spectra with no aftermarket data accessories.
I have the newer style connector, the "db25 on steroids" as you described it. The cable I have is stamped with the part number FKN-5850A and on the other end it terminates in a rectangular white plastic fifteen pin plug.
Hopefully I didn't dumb things down too much. Some people don't understand what a D-sub is.
FKN5850 is an "SSM MAIN CABLE (15FEET)". SSM = Smart Status Message, a DEK look-alike which is used to transmit MDC messages. If you don't know what this is and don't have one, this cable isn't useful to you.
Already connected to this white plastic plug is a pigtail labeled with the part number FKN5852A and the other end of it terminates in the db15 auxiliarly port connector found on the back of the spectra. (speaker audio I presume) There is also a spliced in power connector. I see nothing that plugs straight into the front of the spectra false head.
FKN5852 is an "SSM TO SPECTRA CABLE". Again, if you don't have an SSM, this isn't useful.
On the front of the radio itself I have a false head with long pins that fits nicely into the unit once the little pin extender board is removed. The front of this unit has two db25's, the left one labeled "Control Unit."
Yes, you need to remove the interconnect board (HLN6285, HLN6066, or similar). You'll want to save this in case you ever go back to dash mount. Your control head should interface to the "Control Unit" port.
The last piece I have is a cable stamped with the part number FKN4752A. It has two db25 connectors labeled "P2" and "P3". A third connector on this cable is labeled "P1" and terminates in the infamous Motorola overkill speaker connector. (You know, a db25 molded plastic mostrasity!)
FKN4752A is a "MODEM-RADIO-RIB 3-WAY ADAPTER". You'd use this if you wanted to interface a data modem to the radio, perhaps with a dual control head radio (you run out of DB-25s sooner or later). This is likely not useful to you.
Connecting to the control head is easy enough. I should be able to use the mic jack on the front of the radio and I can tap out the speaker audio from the aux jack port if needed. However, I still don't see anything that wires right up to the front of the spectra body false head straight from the remote mount cable.
Sounds to me like you don't have the cable you need to interface the control head to the radio. Once you get this, on the end that plugs into the control head, you'll have a 2-pin AMP connector for speaker and two wires for ignition sense (orange and green... one for radio power and one for TX enable).
On the radio end, you should have interfaced:
Main A+ to big power connector
Antenna to mini-UHF connector
Remote head to "Control Unit" plug
On the control head end, you should have interfaced:
Microphone to either front or rear plug
Ignition sense to orange/green wires
Speaker to two-pin AMP connector
Radio deck to "RADIO" plug
It sounds like you have a radio removed from a command vehicle, ambulance, or something similar. In lots of cases, the remote cable, which snakes a long way through the vehicle, is simply left in place or cut in the middle, torn out, and discarded.
If you're going to Dayton, I bet you'll be able to track down the cable you need...
