I use a 24V laser. I not want to share the common ground of two different power supply. If you see the four cable version share the TTL- and Laser GND.
The 3 Pin cable version is connect in my case
+24V --> powersupply same for mesa card
GND --> powersupply same for mesa card
PWM + --> + 220 Ohm resistor -->TB1 PIN4 on 7i85s card last axis out
In your case different. Depend on your flashed bitfile. But verify this connection by scope measurement. I searching long time for the right pins.
Laser power control is working over dummy axis. If i set W-axis to -4 laser have full power. It works not so bad but for real picture engraving is my mashine to big and slow. For real vector control works good.
My changes could you read here.
forum.linuxcnc.org/plasma-laser/42872-la...e-mesa-card?start=10
streamable.com/ovpkk1