How to get 12 volts from a Cessna 310?

I have a friend who has a 1978 Cessna 310Q. (At least I think he told
me it was a 1978 model). Here is the question: He wants to plug in
some electrical equipment, a computer and a GPS unit into the cigar
lighter plug. The aircraft has a 24 volt electrical system. He has
been told that the cigar lighter voltage has been dropped to 12 volts
because there is a large resistor in the wire that feeds power to the
cigar lighter. When he checks the voltage at the contacts of the
lighter receptacle, he finds 24 volts. We think that this is because
there is no load on the circuit, and if there was, the voltage would
drop due to the inline resister.
However, he reports that when he tries to run both devices from the
power from the cigar lighter, it does not seem to work.
Any ideas on what to do in his case would be appreciated.

Thanks.


Zenith CH-300 Driver.