Pins counted from bottom of the phone:
1. - GND
2. - Audio Dock output
3. - Audio Dock
4. - Dock ID
5. - Re-charge
1. - GND: It's a common ground of the phone. Using as "-" while charging, GND or COM for audio signal, physically connected to pin5 [GND] on microusb port
2. - Audio Dock output: In dock mode - analogue audio output (channel left) while playing music. When phone is triggered in dock mode, it can be used to play audio on earphones or connect to external amplifier. During phonecall : speaker out [mono]. In car dock mode - not testet yet. Data transmition - not tested yet.
3. - Audio Dock : In dock mode - analogue audio output (channel right) while playing music. When phone is triggered in dock mode, it can be used to play audio on earphones or connect to external amplifier. During phonecall- [not tested yet]. In car dock mode - not testet yet. Data transmition - not tested yet.
4. - Dock ID : Pin used to informing phone what is connected to it (resistance checking). Working only when pin 5 is connected to +5 volt and pin 1 to GND (when phone is on charging). Connecting pin 4 to GND with resistor 10kOhm trigerring car dock mode (resistor have to be connected all the time). Connecting resistor 1,1kOhm trigerring dock mode, don't have to be all the time, ones dock mode is on, resistor can be disconected, phone will stay in dock mode until power (+5v to pin 5) is connected.
5. - Re-charge : Physically connected to pin1 [VBUS] on microusb port. It's used to charge phone by connecting +5 volt. This is USB charging (500mA max), I'm trying to figured out how to force AC charging on it, but may be not possible, maybe HTC has blocked this funcionality because it can be danger for pogo pin ( 1 A throughput).
Post will be updated when we'll find out something more.
Thanks to: @pehkblui , @neovius and all others trying to help