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I picked up a bright red LED recessed in a small chrome ring that I want to install in a Corolla. I wanna add that LED in place of the reverse beep.My question is what will I need to wire up to allow that 1.7volt LED to work on a 12v system? Just a simple in-line resistor? Transistor with a heat sink, or what? It's been 9yrs since my electronics class!

All you need a resistor in series with the LED. (EDIT assuming you have a signal that's 12v when you want the LED on and 0 volts when you want it off. +12V below would be that signal)+12v -------VVVV------LED------GNDor +12v -------LED--------VVVV----GNDWhere "VVVV" is the resistor. A resistor value of about 600-630 Ohms should work fine, assuming it's a 20mA LED (pretty standard)Just make sure the "Anode" side of the LED is connected towards 12v or it won't light up.

Great! Thanks for the explanation and recommendation! Does it matter if the resistor is rated at 1/4 or 1/2 watt?

Quote, originally posted by Mase »Great! Thanks for the explanation and recommendation! Does it matter if the resistor is rated at 1/4 or 1/2 watt?Oh yeah! Great question. Make sure you get at least a 1/4Watt. If you can get a 1/2 W easily, go for that. (But anything higher would be a waste)

if 1/2 watt resistors aren't easily available, you could either put two 300 ohm resistors in series or two 1200 ohm resistors in parallel to share the heat. Not sure if what we call 12V is really 12V, some cars I've had 12V was really about 14V when the car was running, so if a 600ohm resistor has to drop 12V, it will be eating right at about 1/4 watt.Looks like the reverse signal is +12V while in reverse. for reference, in another thread, ragingfish compiled this list of reverse beep disable threadshttp://forums.genvibe.com/zerothread?id=1045http://forums.genvibe.com/zerothread?id=2585http://forums.genvibe.com/zerothread?id=2940http://forums.genvibe.com/zerothread?id=1267