Halloween Decoration PIR Control with Arduino Nano

Hey everyone!

Just joined the community today! I have a problem with a project I am doing. My friend asked me for a favor, if I could make this push button to activate Halloween decoration a movement detection activated one. I have an Arduino Nano with ATmega328 hooked up to a PIR sensor and have written code that when motion is detected, turn on the output. I have tested this with an LED and sure enough when motion is detected, the LED (output) turns on, then when the motion ends the LED turns off, so the code is working, from what I can see, just fine. I have removed the button from the Halloween decoration and had a look at how it registers the button press. There's 3V going through the wires and when the 3V goes in to the other end it triggers. I tested to see if I could run 3V just down the end wire, and no luck. From what I can see the 3V from the decoration itself needs to be run through it as it's not just a simple microcontroller 'if input on'. So I had a look at transistor switching and I have a BC337 (from what I know is a general purpose transistor) and so I have connected the 3V to the collector and the other wire of the decoration to the emitter and the Arduino Nano is connected to the base with a 5K resistor, however when the motion is triggered and the LED, if it was there, would turn on, it doesn't trigger the decoration. I don't know what I am doing wrong here. Any help would be greatly appreciated :)

Thank you for your time,

Tom