Arduino Uno and PWM on 11 & 3

Hi, my name is Peppe and I need to start using a cnc machine with a laser module (15W).

I use an Arduino UNO with Shield v3.0, a 15W TTL laser, firmware grbl 0.9 and software grbl v3.0.10.

As you can see on 2 photos attached, I need to connect the shield board to the laser module board.

There are a triple connector (-12V+ TTL/A), a switch (A/TTL) and a connector (-TTL/A+) on the laser board.

There is a couple of white wirings on pin 11 (ENDSTOP z+) on the shield v3.0.

I have connceted the pin 11 (2 white wirings) to the connector (-TTL/A+).

In this way the red wire of the triple connector is not connected.

Result is that LASER engrave as a B/N and not as a grey scale.

On the laser board there is a blue trimmer with a screw...the problem can dipend from the right setting of it?

Can you Help me, please?
Thanks a lot in advance

the 3 attached