Charges at home on a usb port but not in the car
You should check your car's fuses to see if the one that supplies power to your USB charger is still good. If you're not sure how to do this, you could try plugging a different device into it and see if it works. If it doesn't - you'll need to inspect the fuse or wiring. (you could also try the charger in a different port or different car to see if the issue is tied to the charger).
If the other device does work, it is possible that the charger has a built in fuse. If the charger is the type that plugs into your cigar lighter, you may find the the tip holds the fuse. The tip may reveal the fuse if unscrewed from the body or may require a screw driver to open the body. Either way, you'll need to ascertain if there is a fuse in it and if so, check its condition.
Sometimes, the charger needs to be aligned a certain way in the cigar lighter / power port (or outlet) due to the way some automakers and device manufacturers design the connections. Repeatedly remove and replace the plug in the lighter / port. Each time, turn the the plug slightly so that it takes 6 to 8 insertions to rotate all the way around in the outlet. This should provide at least one position that allows the plug to make the required contact in the lighter / power port.
Lastly, make sure that there is no foreign object / debris in the outlet, that the the plug fits snugly in the outlet, the the plug's tip has a spring pushing it forward and that the plug is fully inserted into the outlet.
Hopefully, one of these suggestions will get it working. Good luck!
Navman S30 Car...
on Mar 22, 2012