So I already have HIDs installed in my car and want to do a retrofit this summer. I've been reading up on it a lot and feel like I have a pretty good understanding but want to make sure I won't be missing anything when I order. I'm going to order just the projector to save some money. All I'll have to buy is the projector, shroud and bulbs right? Since I already have hids I won't be missing any crucial pieces?