The pinout for the COM connector for our units is attached.
Do not connect anything to the +12VDC output though as you could cause internal circuitry damage to the 778cX HD unit. This is meant to power the Humminbird brand accessories and may not be able to provide the power levels that other devices need. It looks like your device is powered by 5 volts, connecting it to the 778cX HD unit may have caused it damage as we output 12 volts and not 5 volts as your data suggests.
The USB Pinout:
| Pin | Name | Cable color | Description |
|---|---|---|---|
| 1 | VCC | Red | +5 VDC |
| 2 | D- | White | Data - |
| 3 | D+ | Green | Data + |
| 4 | GND | Black | Ground |
