No AM reception for car radio...do get FM reception.
I was having the same problem with a jvc kd hdr 30. I Installed it myself over a year ago and never wanted to deal with the issue. Finally, I decided to take a look at it today.
On my head unit, all wires were connected except one blue one with a tag that says "do not connect to power, for remote device or power antenna only." This unit is in a '97' MBZ E320 with no visible antenna; I think it is part of the windshield. In any case, between the wiring diagram in the manual and the harness that is part of my car, I was left with 2 blue wires to choose from, one with a white stripe and one with a gray stripe. After testing both for power or ground, I determined neither had power with key on or off. Both had high resistance ground when compared to the chassis ground. In other words, I measured between chassis and these wires. First, I took a wire and connected it to the chassis ground and connected the other end to the blue wire coming from the unit while tuned to a local am station. This simply killed all reception am or fm but did not harm the unit. Next, I connected the blue wire with gray stripe of the car harness to the blue wire of the unit and again this killed all reception. Then I connected the blue wire with white stripe of car harness to the blue wire of unit and presto magic I had great am reception.
I am guessing that this blue wire with white stripe must be part of the antenna itself or perhaps is a connection that increases antenna power. Maybe 'power antenna' on tag refers to an actual powered antenna (like as in amplified?) and not as in an antenna that rises up out of fender, as I believed.
This may not help the first person with the question, but maybe it will help someone out there who searches for these kinds of answers like I do from time to time.
JVC KD-PDR30 Car...
on May 11, 2016