update: by luck found and bought the identical head unit off craigslist for $50. plugged it into the existing harness and it worked fine. can't figure out what i did to the old one but the install directions with the new one indicate the line in function only works when using a clarion equalizer rerouted back into the head unit. i am thinking somehow it thinks it is in that mode and is waiting for a line in signal from the EQ to amplify. the clarion site does not have any manuals going back that far and i can't find any way to reset the thing.

anyway, $50 is cheaper than a repair and the new old unit doesn't have a scratched face plate or burned out back lights so i'll call it good.