Without modifications to the amp, you will need a battery in the footswitch to run the light.
You can modify your existing footswitch, or you can buy one already made, something like this: http://www.ebay.ca/itm/Voodooman-FootSwitch-1-Button-W-9V-DC-powered-LED-/380503784108
You can modify your existing footswitch, or you can buy one already made, something like this: http://www.ebay.ca/itm/Voodooman-FootSwitch-1-Button-W-9V-DC-powered-LED-/380503784108