Hi there I'm new to this forum and have need of some information on how to fix my problem. I am building a custom car and want to add a dash mounted external led tach light but, have the unit hidden under the dash and a hidden light. so i bought an external adjustable tach light on ebay but i want to trigger a larger external led light so i bought a 12v 24led 3rd break light that i want to install in my dash vent so when i hit my rev limit it will light up. the circuit board inside the tach light has a single led and i want to know how trigger the 12v 3rd brake light off of the led or off the circuit with a reed relay.
what i want to do is have the reed switch trigger off the red led leg and go to ground on the other side of the relay and then have 12v go through the reed to the 12v b+ side of the 3rd brake light. i hope to use the 12v in and ground coming into the board for the relay and just need to know how much voltage is coming out of the red led and if it will triger the reed switch or not.
the reed switch i was looking at is 5vdc and 250ma will this work in this circuit? if not what and how to make it work thanks
the circuit board
http://images.thesamba.com/vw/gallery/pix/971386.jpg
http://images.thesamba.com/vw/gallery/pix/971385.jpg
the 3rd brake light
http://images.thesamba.com/vw/gallery/pix/971384.jpg