I'm guessing you're planning on upgrading the oem halogen lights with hid's? The hid kits should be plug and play. The only issue you might encounter is finding a suitable location for the ballast. But its nothing that some zip ties and 3m tape can't resolve. Idk much about eBay kits. I've used DDMtuning in the past and I'm very satisfied with the product (my mazda's been using their slim ballast kit for 3 years or so with no problems).
1988 GT - Stock
*SOLD* 2012 GT Premium, Black on Black, 3.55 Axle, HID and Security Package, Pypes Pype Bomb Axle Backs