Topic: Headlight Change TSB Article

[J_Speegle]

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

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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.

[67gtasanjose]

... 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.

A VERY GOOD REASON TO BE PARTICULAR TO YOUR HEADLAMP BULB SELECTION!
The "very common replacements" in today's market can cause many issues on a Driver Car.

[WT8095]

The additional 20W (10W per headlight) at a nominal 12V works out to a total additional current draw of 1.7A.

[67gtasanjose]

The additional 20W (10W per headlight) at a nominal 12V works out to a total additional current draw of 1.7A.

Dave, I'm not sure I understand the intent of your calculations. Are you suggesting the Ford Engineers may have overreacted? Maybe the basic "draw" isn't enough to affect safety or satisfactory performance of a mild 38 amp alternator? (pertaining to: if you simply use the later versions of the day)

My message was more about adding aftermarket Halogen Reproductions onto driver cars WITHOUT DOING MODIFICATIONS TO WIRING and/or SWITCHES.
Since we are Concours, by definition, I'm suggesting it is a little bit more than "just looking ('sorta') correct" (e.g. Drake reproductions)

[67gta289]

My interpretation of Dave's calculation is that the additional draw of 1.7 amps (total 10A instead of 8.3 @ 12V) could be enough to cause the headlamp circuit breaker to trip the light off.  It is not uncommon to have an all original car to have low beam lights that cycle on and off as the circuit breaker trips, cools off, then trips again.

This is also what Ford says in the TSB when they mention the need for upgrades if higher wattage bulbs are used.

Now the question is, what do the current repros draw?

[WT8095]

The calculation was purely informational, to show everyone how much more current the higher wattage bulbs will draw.

There are too many factors for me to second-guess Ford's engineering on what size of alternators were installed for each application. But since they used 38 & 42 amp alternators, it suggests they were working in a realm where a couple of amps may indeed make a difference. I would venture to guess issues encountered would tend to be more towards lack of charging, as opposed to say overloading wires or tripping breakers/fuses. Those are my opinions; I don't have any evidence to support them.

Here's one more thought: The higher wattage bulbs on low beam draw the same current as the low wattage bulbs on high beam. So if Ford designed adequate capacity to drive indefinitely with high beams on (original bulbs), there shouldn't be any problems using only low beams with the newer bulbs. Using the newer bulbs on high beam is where you start exceeding the original design capacity. [for two-lamp systems]

[67gta289]

Here's one more thought: The higher wattage bulbs on low beam draw the same current as the low wattage bulbs on high beam. So if Ford designed adequate capacity to drive indefinitely with high beams on (original bulbs), there shouldn't be any problems using only low beams with the newer bulbs. Using the newer bulbs on high beam is where you start exceeding the original design capacity. [for two-lamp systems]

However the high beam feed (switch on floor) bypasses the headlight switch (with built in breaker).  The additional draw through the switch might be a contributing factor for cycling switches.  It would be interesting to see if the service switches after this date were a different revision and had more capacity.

When I get some time in a few weeks I'll do some testing with a couple different switches, to determine the time-current curves we are talking about.

[67gtasanjose]

However the high beam feed (switch on floor) bypasses the headlight switch (with built in breaker).  The additional draw through the switch might be a contributing factor for cycling switches.  It would be interesting to see if the service switches after this date were a different revision and had more capacity.

When I get some time in a few weeks I'll do some testing with a couple different switches, to determine the time-current curves we are talking about.

[/color]
 
I believe the later headlight switches allow the parking lights to operate in all switch positions, meaning the parking lights will stay on with the headlights too.
My understanding is 69? and older, the park lights shut off when headlights turned on. Maybe 68 & older, I'm not absolute on this.

[67gta289]

[/color]
 
I believe the later headlight switches allow the parking lights to operate in all switch positions, meaning the parking lights will stay on with the headlights too.
My understanding is 69? and older, the park lights shut off when headlights turned on. Maybe 68 & older, I'm not absolute on this.

Good point - the 67 and older (perhaps 68 as you mentioned) headlight switches also had to handle the tail light load.  The front parking lights were off (load not included) when the headlights were on. 

My test would be 67 specific in terms of load.  But I would test each switch that had been collected over the years.

[196667Bob]

Obviously, some Engineer at Ford had the "Bright Idea" that the 1968 bulbs (C8's) and slogan had run their course, and it was time to take illumination to "new brights" - err, I mean heights. Sorry, but just couldn't pass this up. Once in a while, we have to "lighten" things up.

Bob

[midlife]

However the high beam feed (switch on floor) bypasses the headlight switch (with built in breaker). The additional draw through the switch might be a contributing factor for cycling switches.  It would be interesting to see if the service switches after this date were a different revision and had more capacity.

When I get some time in a few weeks I'll do some testing with a couple different switches, to determine the time-current curves we are talking about.

Say what???  The headlight switch passes a signal down to the dimmer switch, which transfer the signal to either the low beams or high beams.  There is no bypassing the headlight switch.

[midlife]

Obviously, some Engineer at Ford had the "Bright Idea" that the 1968 bulbs (C8's) and slogan had run their course, and it was time to take illumination to "new brights" - err, I mean heights. Sorry, but just couldn't pass this up. Once in a while, we have to "lighten" things up.

Bob

Are you saying that those of us running older bulbs are "dim watts?"

[WT8095]

Obviously, some Engineer at Ford had the "Bright Idea" that the 1968 bulbs (C8's) and slogan had run their course, and it was time to take illumination to "new brights" - err, I mean heights. Sorry, but just couldn't pass this up. Once in a while, we have to "lighten" things up.

Bob

Brilliant. 

[196667Bob]

Are you saying that those of us running older bulbs are "dim watts?"

You "hit the nail on the head(lamp)" ! And I too, am one of those "bulbous" individuals who likes to "amp" things up a bit, without getting too "wired" in the process. Personally, I like the looks of the old original (like me), cast in glass FoMoCo script headlamps.

I'll quit now, while I'm ahead(lamp).

[67gta289]

Say what???  The headlight switch passes a signal down to the dimmer switch, which transfer the signal to either the low beams or high beams.  There is no bypassing the headlight switch.

Randy, that was a (bad) assumption on my part, did not look at the wiring diagrams yet.  Based on that there should be no need IMO for any increase in capacity of anything unless one drives around with high beams on all the time.  In other words...what Dave said.