Just had a new Pioneer Stereo installed, all is fine except no AM radio reception. Peculiar thing is there was no AM radio reception with the factory radio either. Any ideas?
It is quite possible that the only person or place that can answer this is whoever installed the new unit.
There is a problem with the antenna or antenna cable. You will not get AM reception without an antenna, you can receive most FM stations with a poor antenna.
^+1. If you have the same problem with two different radios chances are the fault isn’t with the radio.
Take it back to the installer and ask why. They should have checked AM reception as part of the installation. IMO, they should check all the features of the new radio before returning the car to you. You should pay for parts, though, since you had no AM reception before the installation.
Whoever installed the new radio certainly didn’t do a thorough job if he failed to verify that it had AM reception before returning it to the customer.