Both headlamps blew at the same time ?

Ok, go back and double check. Put your meter on ground, and probe both or all 4 ballast terminals with key in "run" Makes sure you got the "highest" reading terminal. This is the one coming from the Ign switch.

Then check the bulkhead connector and the ignition switch connector for drop.

Check your 12V going INTO the ign switch. This must be done under load, that is with key "on"

This 1.6 V is being added to the "properly" regulating voltage of the VR, IE 14V + the 1.6 drop is 15.6 volts at the battery.