wiring a avic d3 to a 2002 dodge ram 1500

There could be a burnt trace on the ground wire of the radio.   When I am checking a radio to see if it works, I connect ground to the chassis of the radio via the large alligator clip on my bench.  The guys at Best Buy probably did the same thing.  I have seen more than my fair share of Pioneer decks that have a bad ground path on the ground wire.  These radios will work if grounded through the antenna or through the chassis in some applications.  If you use the chassis of the radio as a ground reference for the meter, this will tell you if the radio is grounded or not.  If you use chassis of the vehicle as a reference for your meter, you will only be testing power and ignition.  I usually tell people to use the chassis of the radio when performing these tests. I must have forgot to mention it here.