Both the 3 amp on-board and 3 amp off-board chargers flash a steady red light if there is an abnormality with the charging system. Generally, this occurs when the charger does not receive a signal from the batteries, in other words there is a break in the connection between the charger and batteries. Check the battery cables to confirm they are connected (black and red plastic connectors), check for loose connections, check the in-line fuse boxes for blown fuses (replace as necessary), and check the reset button (circuit breaker). If you are unable to locate the problem, consult your provider.