okay you need to find out if that is a latching switch or a non latching switch. latching switches are on off stomp switches. non latching are momentary switches, off normally then on only while being pressed.

you can figure this out by your manual usually or a little research. after brief researching i found that the switch you need is latching.

buy this http://www.smallbearelec.com/Detail.bok?no=24 and connect one of the middle terminals to the one terminal of this http://www.smallbearelec.com/Detail.bok?no=558 and one of the other terminals on the switch, same pole, to the other terminal on the jack. install in to an enclosure like this http://www.smallbearelec.com/Detail.bok?no=50
"3. FOOTSWITCH JACK SOCKET The footswitch jack socket (rear of amplifier) enables channel switching using any latching footswitch."

I Googled "Orange TH30," the first result was the .pdf with that. Without an actual schematic (which judging from the other google link on the orange amp forum, you'll need to contact them) I would assume that you'll just need a DPDT switch, on pole shorts the hot of the jack to ground, the other controls the LED. Your best bet is to contact them and see what they use for the switching logic.