Thank you for your input!
Sounds like I've been following the correct procedure.
- Adapter plug into ECU dianostic socket, positive and negative alligator clips attached the the positive and negative terminals of the battery (tested current flow by multimeter across the alligator clips themselves.
- ODB2 cable into adapter cable. No light on ODB2 cable.
- ODB2 cable into USB OTG cable. No light on ODB2 cable.
- Ignition on, wait couple of seconds for initial turn-on.
- USB OTG cable into phone/tablet. Only now the red light on the ODB2 cable comes on.
- Start TuneECU.
- Press ECU button.
- Prompted to turn on Bluetooth. Regardless of bluetooth turned on or off at this point, the connect option at the top remains greyed out. I think it's asking for Bluetooth because it can't find anything via USB, so assumes Bluetooth as the next connection method.
USB Debugging is definitely turned on - I'm a custom ROM user from way back, Developer Options and USB debugging on soon after a new ROM.
I've noticed the diagnostic plug I'm going to (which sounds like the right one) only has two wires going into the back of it - is this normal? I would have thought it would have had a few more...
On the subject of when the red light should come on on the ODB2 plug, it definitely comes on only when connected to the phone, not on connection to the (supposedly) powered ECU socket and adapter plug, even with the power connected. Photo before and after below.
Last picture is of the ODB2 cable flipped over. It certainly looks like it at least has the correct stickers on it...
It would be easy to open the ODB2 cable up and check the circuit, perhaps there's something I can spot in there.
Or I just buy an ODB2 cable from Lonelec or another known good supplier.