I got this head unit installed a week ago Kenwood MP5028, now stations I normally got before with the stock head unit are nearly impossible to get now. Someone said they forgot to hook up the antenna is this possible?

 

very possible and more than likely that is it. Just take it back and tell them to hook the antenna up.

 

IF the antenna is connected then its still expected to lose substantial signal. You went from Factory Nissan Diversity to a single antenna.

 

I had the same issue with my Alpine HU, and a helpful guy at a local stereo shop explained it the same way as Don. The stock HU is tuned to work VERY well with the 2-pin antenna system. However, aftermarket HUs don't have the tuning system required to bring the two signals together correctly, and thus they get a terrible signal. I get almost nothing with my HU, and I've tried chaning adapters. No luck. I wish there were an answer to this, but in the grand scheme of things, my mp3 discs do the job just fine.

-Brian