Ok cornman! You solved your problem while I was composing my last post.
re. using your CMoy (or any other electronics) within your vehicle's electrical system: You should assume that your vehicle's cigarette lighter is designed to .... light up cigarettes. It may not be regulated, so that higher (or momentary negative) voltages may be present. It's not only the higher voltage that the vehicle's charging system puts out; an automotive electrical environment is a really nasty place for an unprotected little circuit like your CMoy to be.There are all kinds of ugly spikes (in the KVs), surges, etc caused by other devices connected to the vehicles electrical system. It's nowhere near as benign as connecting to a 9V battery.
The very first mod that I made to Chu Moy's basic circuit was to add reverse polarity protection. It's too easy to just touch the battery's terminals the wrong way around when replacing the battery.There's no guarantee that the opamp, the filter caps, or even the LED would survive even a momentary reverse contact.