M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Electrical => Topic started by: DesktopDave on January 25, 2010, 08:12:12 PM
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I finally got around to resurrecting my dead light up key. I'd seen a tutorial somewhere out on the web and decided to try it out myself.
All I needed was a 5mm yellow LED and a 3v lithium battery. In order to fit it had to be smaller than the usual PC-type 2032 backup batteries (20mm dia, 3.2mm thick). I found a thin 16mm battery (1612?) that worked perfectly inside the button. I have spares if anyone wants to try this out.
Be sure you get a 3v lithium cell, some coin cells are alkaline with the usual 1.5 volts...not enough to light up a LED.
I took the key apart, removed the dead incandescent light, trimmed & bent the LED lead to fit, then found a foam button that would keep the metal BMW tag inside the button. I clamped and drilled the light socket in the key slightly, and trimmed the LED flange a bit to make it all go back together. BTW, that little bulb compartment is just about the perfect length for an LED.
I decided on yellow instead of red because it's far brighter. The blue or white would have been nicer than yellow, but they require more than 3 volts of current that one lithium cell can provide. You could stack two & overdrive the LED for brief periods.