A recent discussion in the Boss section brought up the subject of when the design of the headlights changed for Mustangs. Since this applies to all Mustangs I choose to post the meat of the TSB article here so that it could be easier found by members in the future and to share the information
Published in a mid March 1972 TSB
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
NEW HEADLAMP BULBS
1972 ALL CAR LINES
New headlamp bulbs were installed on all passenger vehicles built January 3,1972, and later. The wattage of the 5-3/4 inch lamp (low beam) and the 7-inch lamp (hi & low beam) has been increased. The Mustang, Cougar, Maverick, Comet and Pinto vehicles required changes to the wiring harnesses and/or components to accommodate the new bulbs. The Lincoln, Torino and Montego will have an upgraded charging system and components due to the new bulb. Only the Ford, Mercury, Thunderbird and Mark lV harness and components remain unchanged with the new headlight bulbs. lf the new high wattage bulbs are used on vehicles built before January 3, 1972, it is possible to draw more current on some vehicles than the alternator is capable of putting out, thereby discharging the battery and creating a no-start condition. ln addition, on cars with 7-inch headlamp bulbs, the higher wattage bulbs may cause the headlamp switch circuit breaker to operate. lt is imperative that only the appropriate specified headlamp bulbs be used when replacements are made. Refer to the following chart for bulb identification.
NOTE: The new bulbs will have 1/8 inch flutes for positive identification in comparison to the preceding bulbs having 1/4 inch wide flutes as shown in Fig. 14.
(http://www.concoursmustang.com/forum/gallery/5/6-080316221823-5344285.jpeg)
(http://www.concoursmustang.com/forum/gallery/5/6-080316221825-5345781.jpeg)
Must be a typo in the TSB, the 7" lamps and the 5 3/4" lamps do not have the same engineering number stamped on them.
I have had the problem of headlamps cycling off then on when I foolishly installed four Halogen bulbs in a '67 Cougar. Also had the same issue with the tail lamps in the same car when I - again foolishly - installed six 1357 bulbs in place of the original six 1157 bulbs.
A recent discussion in the Boss section brought up the subject of when the design of the headlights changed for Mustangs. Since this applies to all Mustangs I choose to post the meat of the TSB here so that it could be easier found by members in the future and to share the information
Published in a mid March 1972 TSB
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
NEW HEADLAMP BULBS
1972 ALL CAR LINES
New headlamp bulbs were installed on all passenger vehicles built January 3,1972, and later. The wattage of the 5-3/4 inch lamp (low beam) and the 7-inch lamp (hi & low beam) has been increased. The Mustang, Cougar, Maverick, Comet and Pinto vehicles required changes to the wiring harnesses and/or components to accommodate the new bulbs. The Lincoln, Torino and Montego will have an upgraded charging system and components due to the new bulb. Only the Ford, Mercury, Thunderbird and Mark lV harness and components remain unchanged with the new headlight bulbs. lf the new high wattage bulbs are used on vehicles built before January 3, 1972, it is possible to draw more current on some vehicles than the alternator is capable of putting out, thereby discharging the battery and creating a no-start condition. ln addition, on cars with 7-inch headlamp bulbs, the higher wattage bulbs may cause the headlamp switch circuit breaker to operate. lt is imperative that only the appropriate specified headlamp bulbs be used when replacements are made. Refer to the following chart for bulb identification.
NOTE: The new bulbs will have 1/8 inch flutes for positive identification in comparison to the preceding bulbs having 1/4 inch wide flutes as shown in Fig. 14.
(http://www.concoursmustang.com/forum/gallery/5/6-080316221823-5344285.jpeg)
(http://www.concoursmustang.com/forum/gallery/5/6-080316221825-5345781.jpeg)