Hi,
The message you linked shows the correct jbc connection.
Yes, you could use one of the gnd wires (3/4) for that.
But you'll have a hard time desoldering that connector!
The easiest way would be to cut the pin, so it doesn't reach the board, then solder a wire to it.
Once you do that mod, you'll have to fix the T12 handle, joining both gnd wires together into the same pin, also T12+ with the pin you'll be using as tip temperature sensing (3).
Another approach, tidier and easier, would be this:
Since the T245 handle has no NTC, you'll have to disable it in the settings, so it uses the internal temperature sensor.
Now you can repurpose the NTC pin with few little modifications:
- Remove R10 so the CPU becomes isolated from the NTC pin.
- Cut the trace on R0 to isolate the amplifier from the tip power pin.
- Join the NTC and temp. sense pads.
- Now use the pin 2 for the tip temperature sensing, all should work fine.
The T12 handle would need to be fixed, disconnecting the NTC and joining T12+ with the pin 2.
Disabling the NTC doesn't make a lot of difference, perhabs some °C, but nothing crazy.
Check out your board
schematics.