Before you plug your equipment into the cigar lighter of your new (or an unknown) car, it's a good idea to test the lighter polarity. Fig shows a simple means of doing this. The circuit tests for a center positive condition at the lighter; if the lighter is powered, and + 12 volts is connected to its center contact, DSllights. Carry this gadget with your "pluggable" 12-V gear; it could save your transceiver from a quick demise.
The actual device is slightly different from it looks in the photo, with rounder edges. The voltage beat is advised for all vehicles and can read from 0 - 24 volts.
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