1996 chevy s-10 ex-cab , cig lighter w/2 augzillary plugs. When I plug in my Garmin navagational device it will drain the batterie dead in just minutes if I leave it pluged in after I turn the moter off. No matter if I use the cig lighter or the aug.

One of 2 things can be going on just off the top.

1) Your battery is weak. (check the rating on it and have it tested if its a few years old.)

2) You could have a short that is causing it to run high amps and you will need to test that with a amp meter.

Remove and fully charge the battery. Most auto parts stores will do this for free. I would also check the alternator--regulated battery voltage across the terminals should be 14 to 15 volts, while the engine is idling. Be sure to clean the battery terminals, cable connections, and main ground. Check the cables carefully for hidden breaks or corrosion.

Checking your battery is a good start, how old is it? Checking the positive cable couldn't hurt either. Then go from there. Routine maintenance stuff.