As mentioned, you should at least have the radio "hold off" transmit while there is activity on the channel.
Maybe you planned that, but if not, most of us I believe are going to recommend that.
As for Maxtrac connections, yeah, all you could ever want to know is on Repeater-Builder or Batlabs.
To save hunting:
KPC-3 function Maxtrac MIC Maxtrac logic board J8 if 16 pin logic board
1 Tx aud 5 12 2
3 PTT 6 11 3
5 RX aud 8(fixed level) 4 11
6 gnd 4 10 7
6 hang up button 3 13 not available
COR if needed 8
Note that many Motorola products number the mic pins backwards. The above list for the Maxtrac mic numbering is looking at the FRONT of the radio, the release notch is to the right, contact pins to the left, number 1 is at the top, 8 at the bottom.
And as usual, check these for yourself prior to hooking up, I am not responsible for errors, just trying to help.
I like using the logic board J8 connections as I can solder direct to the pins ( one less connector to buy and possibly go bad. And those connections work with the old (cheaper) 5 pin logic board radios.