Wiring an EasyJake 2006 Freightliner M2 w/ CatC13

Where do I find the tire to break the connection to make the jakes work intermittently from a switch on the shifter? I'd like to use a momentary switch. I unplugged one wire at a time off the back of the two stage switch on the dash and none would brake the connection to the jakes. If I unplugged the switch the jakes would be on hi. There is about 5-9 volts depending on the polarity of the multi tester on most wires. I'm stumped on how to wire an EasyJake into the system. Any proper help would be appreciated. Thank you Bob

 

I know how to wire a relay. But I don't know what wires to connect to.