Charging 12-volt = posts clean, battery fluid OK, following instructions for a NEG GROUND. I can hear charger "hum" Charger is 2-LED model Red LED is ON showing power source OK Yellow-to-green LED is not "yellow" to indicate cables are correctly hooked up Positive aligator is attached to cable collar (?) around positive post (clean) Negative aligator is attached to block - not sheet metal Why is the yellow-to-green LED not working? Thank you K