Do I fill my radiator on my 2003 Honda Sabre with it running or with it turned off?

You should fill the radiator of your 2003 Honda Sabre with the engine turned off and cool to avoid burns from hot coolant or steam. Open the radiator cap and add coolant until it reaches the proper level. Make sure to check the overflow reservoir as well, and only run the engine after filling to allow the coolant to circulate properly. Always consult your owner's manual for specific instructions regarding coolant levels and maintenance.