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A number of years ago I saw a product that plugged into the cigg lighter socket and fed 12 volts (low current) through the car BUT the brain dead engineers at Benz decided the car didn't need a hot cigg lighter socket when the car ignition switch was in the off position. In the interim, get an alarm or battery backup battery (12v 7amp) and clip POS onto the little black fuse pack ahead of the heater solenoids forward of the battery. Hot to the buss there and of course NEG to a ground. Be careful with taking the battery cables off the car battery (I would still use the NEG cable off first, then the POS), if the POS cable touches any ground (remember the 12v 7amp battery is in the circuit) it may damage something. That will maintain system voltage for the short time the car battery is being replaced. After the new battery is installed and connected properly, just unclip the 'HOLD' battery wires (for lack of a better term?).


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