Both headlamps blew at the same time ?

You probably have voltage drop in the ignition harness. With key in "run" but with engine off, find your 12V switched ignition. Leave one probe on that connection, put the other probe on the battery positive post. If you read more than .3V (three tenths of one volt) you have drop in the harness. This drop ADDS to the VR setpoint.

15V is not enough to blow up headlights. It IS enough to boil a battery.