This is a part for airsoft P90s, it replaces the trigger of the p90 with an identical one but with a housing for a standard mechanical keyboard switch and holes for wire passthrough. The position of the wire passthrough hole is right where the spring for the trigger is located, so you will want to remove that.
Additionally you will be removing the linkage bar and if you want to save some weight, I recommend removing the stock trigger contacts as well as they will be unused after installing this.
This is intended to be used alongside a MOSFET/FCU.

This will make most p90s full auto only unless you use a MOSFET/FCU which has a fire select/semi auto mode.
This also disables the safety from actually doing anything to prevent firing. What I have done is wire a simple switch in between the trigger and the MOSFET, located in a small cutout on the mock casing ejection port on the bottom of the grip. This will interrupt the circuit to the trigger, preventing it from firing when the switch is open.

I recommend using heavier weight switches as most switches make for an extremely light trigger pull.
I find this to be uncomfortable when the trigger is in the safe position, but to be perfectly fine when the trigger is in the full auto position.

No hardware needed.