| Pin | Pin Name |
Description |
| 1 | +5V | 5 volts DC |
| 2 | data | not connected / float |
| 3 | data | not connected / float |
| X | GND | connected to pin 4 (GND) with 17.3K ohm resistor |
| 4 | GND | ground |
Standard 5 pin mini-USB connector has pin X connect to ground (pin 4) through a 200K ohm resistor (Note: The normal USB connector has only 4 pins, the mini-USB has 5 pins). To place Nuvi into charging mode, the 200K ohm resistor must be changed to 17.3K ohm. (also successful with 22K ohm resistor from Radio Shack, also a cheap 1/8W, 5%, 15k ohm resistor will work just fine!)
Nuvi behavior depends on mini-USB plug connection. (IMHO) it is like this:
pin X not connected - data cable, nuvi connects to PC as removable drive, navigation NOT possible.
pin X & 4 short-circuited - USB supply 500mA, possible navigation,
pin X & 4 connected through 18kOhm resistor - Garmin supply 1A, possible navigation.
I personally modified a cable that connected pin X to pin 4 (shorted), and verified the 500 mA charge behavior as noted above.
Nuvi requires 1000mA for simultaneous charging + GPS operation [many 'generic' 12VDC-to-USB adapters output a maximum 500mA]
Garmin Oregon requires a resistor of at least 47K ohm for running in external power supply mode (100K ohm also works). Smaller values are working, too, but Oregon then first shows a message that an unsupported accessory was found.