tig amp controller

[flamephil]

hey as said earlier, i bought an old 1676 miller econo twin hf 150amp!!
i built a on/off hf switch for arc starting...
now i want a foot pedal to control amp output!!!
i have no plug in on my welder to do that so i want to run it between the welder and the torch!!
i know other people post that before but it was not clear enough for me!!
so is there anyone who knows exactly what to do??
any help would be appreciated!!
thanks