launch controller continuity tester


Well-Known Member
Jan 20, 2009
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Most LEDs have a maximum recommended current of 20 ma.

This current is safe for most, if not all igniters.

A very simple approximation for the correct resistor is V/I = R

I = 0.020 amps. For V = 12 volts: R = 12/0.02 = 600 ohms. This is the resistance value that will limit the current from a 12 volt battery to the ignitor to 20 ma even if the LED shorted out.

This does not count the resistance of the LED, so it's conservative.

You can use any resistor with a resistance of 600 ohms or higher.

A 1000 ohm resistor in series with an LED will allow ~ 10 ma current. These are easy to get at any Radio Shack or similar electronics store.

Bob Krech