Just some feedback on that DIY. I don't like it. If I'm reading it right it looks like that piggy back connection doesn't truly connect the wires together. The only thing holding it together is a bit of pressure from the wires being side by side in the connector.
The other thing that bothers me, and no offense to the guy who wrote it, is that he is not sizing his connectors properly. Yellow connectors are typically for 12-10 gauge. I would have went with blue or red. Being a 12v guy, I buy every connector in those 3 colors and only use the appropriately sized connector. Otherwise your connections are loose. Loose connections are bad.
What would have been better is if you would use a 3M Scotchlok T-Tap or maybe even better still a squeeze connector like in the picture below.
Scotchlok
I'm not sure what that green/white wire is supposed to power so I can't comment on how safe it is to use that wire. But it would be good to find out so that you don't exceed the current that is supplied by that wire. Ideally, you would have a dedicated 12v connection for the hardwiring. That's not always convenient so you can compromise a lot of times by tapping into other wires. Before you do that, it's usually a good idea to know what that wire is used for.
So the safer method right now is to go with the fuse tap on a heftier source like the ignition.
Ok, off the soapbox for now...