Depending on how they are wired you most likely have a bad ground or possibly a bad turn signal switch. Hard to say for sure without a schematic and checking the circuits but the corrosion wouldn't cause this. The corrosion could cause an intermittent no start or a weak cranking but it wouldn't affect individual circuits. Also as Random Thoughts said, if by bad you mean the right side blinks really fast then you have a bad bulb. My earlier statement about a ground or switch is if they aren't working/blinking at all.