[InvisiBill]

Just to clarify, the amperage rating just tells how much the circuit is capable of handling. The load "pulls" current from the source. You can have a device that pulls more than the circuit can handle (think of hooking up a huge headlight array using tiny little wires), which can overheat the wires and lead to fire. But hooking up a small load with huge wires (think of a single LED light hooked up with jumper cables) will still only be flowing the tiny amount of power needed for the LED. Make sure your power source and wiring are rated at least as high as your load - overkill is not a problem.

The white wire is just connected to the battery through the 30A main fuse in the starter solenoid. If it worked fine when hooked up to the battery but not when on the white wire, you either have a problem with your stock wiring or there was something else weird going on (bad connection, short, etc. somewhere).

According to the wiring diagram, the accessory leads are connected to a fuse in the junction box powered directly by the white wire. If you're not using them for something else, they should make a great power source for this. Otherwise, the white wire going into the ignition switch or wired up directly to the battery terminal with a fuse should give you the exact same results.