To do mine I used a pin from a spare climate control unit plug I didn't need.
I went to radio shack and got a cheap
SPST Push On-Push Off Switch.
Pushed the pin into the slot on the tcu plug:
Grounded the other end to a screw under the dash into the frame.
Mounted the button the back of the steering wheel.
Later on I bought a spare one of these things:
Removed change holder on right side of steering wheel and replaced with switch panel.
There is a screw behind the change holder that I used as my ground.
So for now it looks like this.
Eventually I am going to grind it down some more to recess the button so I can glue the button cover onto it. Just to damn lazy..
And still debating what to put on the left side switch, maybe on/off switch for a zex kit someday...