My players would like to add some sort of small auto-blaster or light laser cannon to the front of their YT-1300, and give the pilot the ability to fire it. Seems legit to me, but I want to be sure I handle it right mechanically. Is it as simple as not allowing him to do piloting actions if he chooses to shoot? Should there be any additional drawbacks to him concentrating on shooting what is in front of him instead of piloting?

I wouldn't add any penalties.

As with starfighters, if the pilot chooses to use his or her Action for attacking with a vehicle weapon, s/he cannot make any other skill checks or Actions.

My players would like to add some sort of small auto-blaster or light laser cannon to the front of their YT-1300, and give the pilot the ability to fire it. Seems legit to me, but I want to be sure I handle it right mechanically. Is it as simple as not allowing him to do piloting actions if he chooses to shoot? Should there be any additional drawbacks to him concentrating on shooting what is in front of him instead of piloting?

Nope, burn the HP and add whatever you like. Easy peezy.

Is it as simple as not allowing him to do piloting actions if he chooses to shoot? Should there be any additional drawbacks to him concentrating on shooting what is in front of him instead of piloting?

Just to be clear, most things a pilot does are Maneuvers, not Actions. So generally pilots can fly around while firing weapons without penalty. Like when in an X-Wing. Also, if you are short handed, it's possible for the pilot of a YT-1300 to fire one of the turrets from the cockpit, so you don't actually need to mount a new weapon on the ship unless you've got a full crew.

Is it true that the pilot can fire mounted weapons without penalty from the cockpit? That seems a bit overpowered. They'll have a full crew, so I still think they'll want the extra weapon, but it could be an interesting option if the two smart ones run around doing mechanics checks for awhile.

The pilot could slave a single weapon to a forward firing arc imo. That's not OP I don't think.

I say yes you can as a pilot fire a weapon, but only forward. In RotJ Lando fires the concussion missiles at the reactor.

I don't think every ship has the ability for the pilot to fire weapons. They need to be specifically put together for that to work, although modding an existing weapon to be pilot controlled would be easy.

I think any pilot controlled weapon should be forced to only fire forward while controlled by the pilot. Firing at any other angle would be impossible to do while flying.

I'd also say a pilot could control as many weapons as makes sense. A YT-1300 with a forward mounted concussion missile launcher and a fixed heavy laser? Sure. Controlling all that plus the turret weapons? No.