I did use rosin core flux , and i didnt see any evedince of corrosion in the wire , i solder lots of stuff at work in the same manner , i am a transmission tech and am very familiar with correct procedures on soldering, my best take on the situation is the vibration is making the contact on the pigtail arc? it takes a long time before i have a problem again , i have always in the past bought my headlight and pigtail from the harley dealer , and have no aftermarket accesories wired in, thanks so much for any input from you all , Danny