MCI Headlight Wiring - 12-Volt Lights on a 24-Volt System
Many folks are confused about the 12 volt headlights in their 24 volt bus. MCI has a simple explanation buried in their website that I found some time ago:
Early MCI coaches used 24 volt bulbs for all the exterior lights, including the headlamps. During the mid 1980’s the 24 volt headlamps were replaced on the MC-9 coaches with 12 volt headlamps, beginning at unit 34901. By wiring the headlights in series, 12-volt lights will operate with a 24-volt system.
See the whole scoop from MCI Service Information in this bulletin from 2001, along with another Bulletin explaining the procedure to change older 24v headlight systems to 12v. (pdf)
