Hackaday reader [Paul] recently shared a simple hack he put together via our Flickr photostream.
It seems that his Magellan GPS unit is pretty finicky when it comes to power supplies. When connected to the Magellan adapter, the GPS unit charged as you would expect. When connected to a PC, it sensed the connection and allowed its file system to be mounted, just as it was intended to do.
However, a problem arose when he tried hooking the Magellan up to a different power supply. The unit still thought it was connected to a PC, and refused to perform any GPS-related functions since its file system was tied up. Not wanting to lug around multiple chargers, he decided to see what the heck was going on with his GPS unit.
He pulled the plug apart and found that the 4th and 5th pins of the USB cable were shorted together. While most devices ignore the 4th pin, the Magellan checks to see if that pin is grounded. If so, it assumes it is connected to its power supply. If not, it assumes that it should act as if it is connected to a PC.
With this information in hand, [Paul] did the same thing as any of us would and hacked together a USB cable with shorted pins. The cable can be attached to any standard USB port or charger, saving him from having to lug around an extra adapter.