Now that I think of it though I think I did use my ash tray 12V lead. You could use either. I used the 12V lead to run through a relay and allow another switched 12V to come from the fuse block under the drivers dash. That way I didn't have to worry about what was already on that circuit.
I've had a couple questions on this. Let me see if I can give a quick electronics lesson.
Relay-
Noun 1. electrical relay - electrical device such that current flowing through it in one circuit can switch on and off a current in a second circuit
relay
circuit, electric circuit, electrical circuit - an electrical device that provides a path for electrical current to flow
electrical device - a device that produces or is powered by electricity
electromagnet - a temporary magnet made by coiling wire around an iron core; when current flows in the coil the iron becomes a magnet
Below is a picture of a relay.
The purpose of this relay is to turn on a pair of lights. There are 2 circuits here. One that turns on the relay (Pin 85 and 86) and the other that passes through the relay and powers the lights (Pin 30 and 87). Pin 87a is not connected to anything.
You can use the same concept with Pin 85 being your Ash Tray 12V, Pin 86 going to ground. Pin 30 would go to your power (Fused 12V like I did from the fuse block under the driver side dash.) And Pin 87 that would go to your independent LEDS.
I don't know where I will get around to it but I have been thinking about building a basic electrical thread for folks. It would include different properties of electricity and how to install lights, accessories, electronics, etc safely.