[DonRotolo]

Actually, most lighter sockets cut off when the starter is engaged, to protect the equipment connected from the wild voltage transients that come from engaging a highly inductive kilowatt-plus load.

Anyway, to the problem: A simple solution is to make a fortifier. The cigar plug goes through a single diode (1N400x) in the + lead, then to a 12 volt rechargeable battery. A very small battery, smallest you can find. A large capacitor (Rated to 16 volts min) would work, too. The battery or cap is connected across the input, and also leads to your device.

Let me know if you need a wiring diagram or some suggestions for batteries. It should all fit inside a 2x3x5 Radio Shack project box, one end is a cigar plug, and a socket is mounted to the box, so you can use it for anything.

Don