The people that install all the audio systems at Circuit City told me that it was the problem. It makes sense that its the reason the aftermarket headunit wouldnt turn on but the stock one would. Kenwood has a 22 watt amp built in and OEM has nothing therefore Kenwood needs more volts. If I took my car to them to get it installed they would have done the exact same thing. I dont know what instruction manual you would be talking about I looked in the owners manual several times and all I see is crap about how to find a station with the stock radio or put a cassette in.