Batboard

I need help with those radios that i planed to use in a repeater system. Two of those as repeater and the other as a link to another repeater. But i need to have the opportunity to change channel on those two radios that is going to work as an repeater. With the repeater controller i have it is an puls (to ground) that is controls channel change. But, where can i connect that wire on the radios? I think that GM950 and GM350 mybe can be used as repeater, and connect the wire from controller to the wire from the channel button in the front of the radios so when a puls is coming,wil both of the radios change channel at the same time, and a new puls they wil change back again. I planed to use two channels. I know that it have been done before with two gm900, but can it be done with gm350 an 950? Or is it posible to change channels on another way?