I had installed some aftermarket DRM modules a few years ago (here in Canada, they are standard in vehicles since something like 1990) i think they still have these boxes at Canadian Tire.

The module was a small box (2 x the size of a fog lamp relay) with an "antenna wire" that you had to wrap around a spark plug wire (to detect if the motor is running). These modules where used power on some separates running lights, only when the motor is running.