| Pin | Pin Name |
Description |
| 1 | +5V | 5 volts DC |
| 2 | data | not connected / float |
| 3 | data | not connected / float |
| 4 | GND | connected to pin 5 (GND) with 17.3K ohm resistor |
| 5 | GND | ground |
Standard 5 pin mini-USB connector has pin 4 connect to ground (pin 5) through a 200K ohm resistor. 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)
Nuvi behavior depends on mini-USB plug connection. (IMHO) it is like this:
pin 4 not connected - data cable, nuvi connects to PC as removable drive,
pin 4 & 5 short-circuited - USB supply 500mA, possible navigation,
pin 4 & 5 connected through 18kOhm resistor - Garmin supply 1A, possible navigation.
I personally modified a cable that connected pin 4 to pin 5 (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.