Can somebody explain to me why this circuit will not work?
It might be that IRF3205 isn't a great choice for an Arduino but it works for Adam Welch on youtube so it should be possible. Tried it even with a 10k resistor gate to source.

When I measure it when the gate goes LOW: 

- Gate is 0v

- Drain is 3.7v

- Source is 3.7v 

When I measure it when the gate goes HIGH: 

- Gate is 5v

- Drain is 8.7v

- Source is 5v 

EDIT: Missing in the diagram is the ground to ground connections 

[![enter image description here][1]][1]




  [1]: https://i.sstatic.net/0uQoY.png