How to interface Mocom control head w/modern radio?

[Furious440]

Hello everyone,

In attempt to complete a classic squad car restoration I am looking for information on how one could interface a typical Mocom 70 control head, speaker and mic to a modern radio like a GM300? Finding a working or repairable UHF Mocom 70 has been next to impossible for us.
I have heard of this being done. I am only and installer and not a radio tech so I thought I would ask the experts here.

Thanks in advance to all who reply.

[kf4sqb]

You should be able to interface to a GM300, or similar radio, through the accessory connector on the back of the radio and do everything you want to do, provided you have the expanded logic board with the 16-pin accessory connector. Speaker audio, mic audio, PTT, and channel steering are all available in the accessory connector, with the proper programming, although I personally have no idea how to set up the channel steering. I just know its possible. Here's the pinout of the GM300/M120 accessory connector: (Batlabs link), and here's the pinout of the Maxtrac/Radius accessory connector (not much difference): (Batlabs link).

All of the "programmable I/O" pins can be set for different options via the RSS, and are where you can set up "channel steering". Once again, I don't know exactly how to make this work, just that it can be done. I'm also not sure if you can actually control the volume with such a setup, but you should, at the least, be able to change channels, key up, talk, and listen.

Best of luck, and don't forget to post pics of the finished product!

[abbylind]

I hooked up the old radio as it was originally installed in the unit. Hooking up pins 19 and 20 to 12v would get the green and the red PTT lights to work on the Mocom control head. A current model radio could be hidden under the seat or dash and a external speaker could be used for the "radio sound effect"
Might be easier than trying to interphase the old and new one.

Fowler

[FireCpt809]

That is what we did for a show car, they wanted a Motrac to look like it worked. We mounted a maxtrac in the glove box, used a motrac external speaker used an mic extentsion cable that terminated through the motrac mic connector used the amp conncetor as the cover with a heavy duty mic. and wired the lights on the motrac to light up when the car was on. We even mounted a dummy motrac chassis in the trunk . Unless you opened the glove box no one was the wiser.

[KitN1MCC]

another good bet is the maratrac

[Furious440]

Thank you to everyone for all the advice.
I am going to review the accessory connector schematics for the GM300 and the schematics for the Mocom 70 control head.
I already have a NOS Mocom control head, speaker, mic, hang up box, harness and fuses. It's finding a good radio that seems to be a pain.

[techie]

You could also try looking for a Motrac or Motran.. I actually have a working loband Motrac sitting here, with a Mocom-70 head on it.

If you use a Maxtrac, you could probably wire a small relay to take the PTT from the mic, and use it to key the radio, and the transmit light.