Quote Originally Posted by spcw1234 View Post
My money is on "going mad"
I would simply read from the LED cathode through a 10K resistor to the input pin. Put a 22K resistor pulled down to ground also to that input pin. You may be able to use lower values on the resistors without the pull down resistor turning on the LED, but I would think this would work. Hope this helps some...
spcw1234: I owe you a beer or three! 10K on the input and 22K to ground worked but the dim glow on the LED was very noticeable. However 120K on input and 220K to ground seems to work without the glow.

I was sure I actually started with that approach but had two problems that I recall;
1) The LED glowed dimly unless I went very high with resistor value
2) For what ever reason it didn't seem to work with the engine running or at least not reliably.

Still need to do some more testing but looks good so far.