63 Dart AM radio

I just bought a used AM radio for my Dart condition unknown. After cleaning the tuning buttons to unstick them, I tried to power the unit up to see if it worked. I was using only a 12v power supply and did not have a speaker or antenna attached. Volume at lowest level. The light comes on but it flashes off and on. Could this be caused by not having an antenna and speaker attached? I figure maybe the circuit is not under proper load and something is cycling the power. Haven't installed in the car yet to see if that makes a difference. Just wondered if it was obvious it needed repaired or just needs installed before powering up.
Author: admin