Otherwise the main culprit is getting the connections swapped over on the output jack.
I think Simon is onto it there.

What/where is that turquoise wire going to after it comes out of the hole to the jack?
It disappears behind the pickguard in the photo.

You have 3 wires coming out of that hole as well. Generally speaking there's usually just 2, the positive and the ground.
I'm guessing you have 2 grounds going to the jack? (1 from bridge, 1 from a pot?)