wiring to a power source

Hi Guys, I have 'hard wired' a dual cigarette lighter plug to the back of my existing plug (essentially creating three plugs). So far this has worked fine, all three plugs still work. I simply connected the positive/earth to the existing wires that joined to the plug of the original. Is there something I should have done differently of should consider? Or can you simply 'branch' off multiple power-consumers from this main line? Reason is I want to add another powered item to this by branching off the dual plug that is now in the back of the car. I appreciate your advice to this 'newbie' Cheers. JvK

Nissan Stagea 2003

 I will add you can put as many outlets as you want on that circuit, but the fuse that feeds that system will determine th amount of things you can plug in.

If the OEM fuse is 10amps, you cant plug in a series of items that added together need more than 10 amps