Get your light and open it up. Clean battery contacts and any places where wires connect. I cleaned off all of the old wires and I had to clean all of the contacts with a wire brush before I could solder to them. A Dremel works great for this.
Modify the basic wiring of your light to fit you plans.
Step 1: Old Light
Some Professional LEDs have a resister or a circuit in them that controls the current and voltage for that LED. They do not light up until they reach their minimum operating voltage. These LEDs can usually run up to 9 or 12 volts, but test them first. My work light LEDs work perfectly at 6 volts and that is all I needed. I did completely rebuild my light and re-do all of the wiring. My work LEDs were not bright enough through the dome so I moved them to the rim.