Great News for Your Garmin.

[Niel Hoback]

  SIX VOLT SUCCESS!

  I just wired a cigar lighter backwards in my Plymouth to test the carcharger for a GPS.  The housing has to be insulated from the dash as it is now Positive.  The Garmin came on and works perfectly!  ON 6 VOLTS.  Now I have an accurate speedometer.   

  My Craftsman timing light also works on 6 volts because most electronics now actually run on 5 volts.

[Plymouthy Adams]

most of the GPS runs on 5 volt (USB connector)  this is how you power and upgrade...my Tom Tom is such

[TodFitch]

I use the mapping/gps functions on my smart phone as you are your TomTom or Garmin.

 

And I was doing something like that with the power, basically reversed polarity and isolated ground, for powering my smart phone using USB power. However it is easy to get careless and have the end of the USB cable with its exposed ground shield touch things in the car. And most things in the car are metal bonded to the car ground. Result is damage to something.

 

So now I am powering my lighter/accessory plug with a voltage inverter. No worries on having the loose end of the USB cable touch anything. And as a bonus, it cleans up the power over a very wide input voltage range so I don't have to worry about low or high voltage damaging my smart phone.

[Niel Hoback]

  I avoid the loose jack end accidentally touching metal by keeping it plugged into the GPS. Its powered by the accessory terminal on the ignition switch so its not hot with the key off.