Looking for the added tone mod for the Fisher CZ6

[treasurehunter747]

Hello Guys,
I have a Fisher CZ6 that i would like to add the 4th tone to. I have looked high and low and all i can find is that there is a resistor and clipping of some wires but aside from that nothing more. If someone has the information for the modification I would greatly appreciate the help. Thank you and as always... Keep on Diggin
Frank