Convertacom for MX1/2/3000 built 1990

[MX3013]

Hello!

I have a problem. I have a Mx 3013, the same as the saberIII but built for the german police, paramedics and so on.
I want to take it with me in the car with a convertacom.
The Problem is, the convertacom is built for the later MX(1992 and on).

I heard about the possibility to change something inside the box, to use the earlier MX...

It's silly, everythings works, but to switch on and off the radio with the yellow cable is not possible!

Can anybody help me?

Thanks!

Chris