Does anyone know how to wire up an LED light so it's ON at all times, except for when the vehicle is running? I think a relay can be used with a signal from the IGN to kill the power to the LED when the truck is running, but I'm not sure how to do it. Any ideas?

If you're wondering why, this is for an "alarm" blinking LED that I want to be on unless I'm driving; also, I don't want a switch for it, rather it be automatic.

 

Get a normally closed relay. Tap in to the "on" circuit, ground the other switch post, then run a wire from the battery through the relay to the light. Then the light will be on until you turn the key to the "on" position.

 

Cool thanks, I'll try that out.

 

Looks like I can just use a standard Bosch SPDT relay, and use pin 87a for the normally closed circuit.

http://www.coolcatcorp.com/faqs/relays.html

 

^^ that's exactly what I was about to post. You can do that with no trouble.

Curious: Why the constant on? Alarm LED? Interior fan?