reception nightmares

I just hooked up a new aftermarket kenwood stereo in my 2004 kia optima and my reception is poor. I just found out the car has a powerred antenna but I don't know where. I asumed it was built into the winshield. I only had the coax hooked up with the power wire on my harness and radio just taped off asuming it was for one of those power antennas that go up and down . without the power hooked up I got no reception at all. once I relized that car had an ampped antenna I went back in and spliced the power conection for the antenna and now I get reception but its not great. am almost always has noise and fm is ok sometimes but mostly only good on the stronger stations. when I drive it occasionaly fuzzes in and out especialy if I drive next to something or go around a corner and if I park in some spots it gets fuzzy. It was alot better with the stock stereo. actauly the reception was perfect before. I realy don't think I'm picking up engine noise. It just seems its not pulling in a strong signal.the only thing I can think of is that the male end on the coax didn't seem like it would slide all the way down into the female end.if it didn't it was very close but it would go no further and it was snug so I figured thats all it goes. I just spent 2 grand on all these amps and speakers and It sounds great on cd but for all that money I want good radio reception. If anyone has any advice it would be much apreciated.

Exactly the reason I stick with Pioneer head units. Radio Shack sells antenna boosters. You can try that and see if it helps.

The only other thing we could think of is that the radio has a slight defect in it. Attach an aftermarket antenna temporarily and see if that improves the signal. If it doesn't, then it most likely will be a defective HU.

Good Luck!

the harness I bought had a wire for power antenna and so did the radio. are you saying I should disconect that and run a new wire into the car harness antenna conection? wich accesory wire the one thats coming out of the car harness?