Hi @SDI,
I’m not experienced with automotive light bars, so will avoid commenting on that component of the discussion.
It’s worth noting that the Navigator’s PWM driver chip is actually an LED driver. Assuming your light bar is ok with the same PWM frequency as the ESCs are using (e.g. up to ~400 Hz, using the RC_SPEED parameter) then you can just set the relevant SERVOn_MIN and SERVOn_MAX parameters for your output to achieve the duty cycle you want, which you can then feed to your MOSFET. A dedicated duty-cycle PWM converter is likely not necessary (unless you require higher frequencies than the other connected electronics can handle).
You could control that with ArduSub’s built in lights joystick button functions, or alternatives like an on-screen slider in Cockpit.