Most 2 way radio's use 12 volts DC, train cars have anything from 36 to 72 volts DC or even 110 volts AC, derived from 600 volts up to 13K, this then requires special switching power supplies to isolate the radio from the trains power source.
Clean Cab radios are for the most part locomotives only, but years ago you would find CC style radio's on revenue cars also, since they could easily be removed and relocated to another car. NYC Transit had about 2000 custom Motorola or GE radios (Motorola 1964 ish to 1986, and GE 1986 to ?) but over 6000 cars (now 8400+ cars), requiring the switching of radios daily. The engineer was actually issued a radio at the beginning of his shift, but now the days of doing that are over, The FRA now requires radios in all cars and locomotives whether they are being driven or occupied by an engineer or not. On our revenue cars we have a combination of GE Trans R12II, with an old AAR compliant control head, or GE Orion Mobile radios, some with dual head control, M-7100's, and now for the retro fitting of our older cars with radios that wouldn't narrow band (Mitreks) the M-7300 of which the Orion, M7100 and M7300 are actually controlled by cab control heads for TX/RX audio. There is no mobile mic or speaker.
Motorola made many custom radio packages from Motorola Motrac's,Motran's,Micor's,Syntors, and Spectra's, all with custom power supplies, and connections. The ones on the Motrac's and Motrans were really interesting, in that they had an oversize power supply, more power transistors mounted on the side rails and the AAR connector instead of the standard Motrac connector. I was able to salvage 2 of them that were meant for destruction.