Mystery connections for CNC laser

I have a very cheap "Woodpecker" CNC engraver that I got a few years ago (2017ish? ), and just got round to actually using it - working well so far. Lost the manual (which didn't contain much anyway). It uses the "original" woodpecker grbl board - which looks like this
So, the issue I have is the spindle motor is either on or off, there's no speed control for it (switched by a relay). However, it is supposed to provide a PWM signal for a laser module - so with an external board it should be possible to set it to laser mode and just use the PWM to control the spindle motor. This is a thing, and people have done it with more modern versions.
Trouble is, it doesn't generate the PWM signal, so I'm wondering if there's some connection that CNC lasers have that tells the module it's connected. There is a 3 way connector with +12, 0 and what might be PWM, and a second connector with +12 and +10. So I don't know if the 12/10 connector is for a sensor perhaps? Or do I just need to update grbl?
Anyone have experience with these things who can enlighten me?

What version of grbl are you using? The last was V1.1

From this thread, you may need to swap two pins between the arduino and the grbl board, depending on the board and grbl versions..

Also the later firmware changes how things work for laser mode, so you don't need that for spindle control - laser mode does not pause for the spindle to start or stop.

With the correct firmware & pin setup, you should get PWM from pin D11, according to that thread.

Main page here:

Ok. It's at 0.9j. D11 is connected a jumper to select "laser" or "CNC" on the board. The laser select pin goes via a transistor to one of the headers (which I eventually identified as being for DC or PWM type laser connections, to answer my own original question!), the CNC select pin goes via an opto-coupler and another transistor to a relay, which turns the motor on or off.
I tried scoping the D11 signal in the "laser" position when running the spindle with M3, but there's no PWM there. So it looks like an upgrade to 1.1 is in order.