No Low-Beams '94 f150

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MW - 19 Apr 2006 00:16 GMT

Drove to a restaurant with low-beams. Ate dinner. Started truck to go home.
Now low-beams. High-beams work great (to the annoyance of everyone in front
of me...), parking lights work great. I highly doubt both low lights would
go out at the same time. I checked all the fuses - interior and exterior
(even though only a few might apply).

Any ideas? Besides the stupid switch. Why does every vehicle I drive require
a new headlight switch.. RRRR (you don't have to answer that..)

Thanks for any help offered.

Mike W.

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MW - 19 Apr 2006 00:23 GMT

Okay, I'm looking at the wiring diagrams on www.eautorepar.net (Mitchell
site - great site). It shows the main switch flowing to the multi-funciton
switch, then to the headlights. The multi-function switch was replaced
because my wipers weren't working. So I would assume this isn't it. Maybe I
shouldn't assume that.

But when I flip the main switch from parking lights with no headlamps to
WITH headlamps, the parking lights flick off in between locations on the
main switch, indicating to me that it recognizes the switch to headlights.

MW

> Drove to a restaurant with low-beams. Ate dinner. Started truck to go home.
> Now low-beams. High-beams work great (to the annoyance of everyone in front
[quoted text clipped - 8 lines]
>
> Mike W.

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putt@webtv.net - 19 Apr 2006 13:27 GMT

>The multi-function switch was replaced

A clue! Maybe when the multi-function switch was replaced, one of the
wires didn't terminate tightly? Came loose when you weren't lookin'.
More likely than a faulty new switch, but with parts these days....I
wonder what was wrong with the old-time high/low headlight floor switch?
Prolly too reliable....

Dave S(Texas)

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Whitelightning - 19 Apr 2006 17:12 GMT

>....I
> wonder what was wrong with the old-time high/low headlight floor switch?
> Prolly too reliable....
>
> Dave S(Texas)

spoken like a Texan (smile). They have a problem of shorting out in northern
climates, something to do with snow and salt being tracked into vehicle in
winter months. Also corrosion issues for the same reason. Dodge had some
serious problems with fires because of that in the mid 70's to early 80's to
the point that while in the service we were issued a "modification work
order" to ether remove all the insulation from the floor mats, or remove the
floor mats completly for all M880 and M890 series 5/4 ton Dodge trucks..
All they did is move the darn thing up on the steering column and run a rod
down to it from the stalk. I replace a lot less highbeam switches since the
move was made. Another easy money repair lost.

Whitelightning

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MW - 19 Apr 2006 17:41 GMT

I just cannot believe it..... Both bulbs burnt out at the same time. Went to
the local parts store, bought new lamps, threw 'em in... bingo. I am
relieved, but bewildered. Maybe God graciously did this so I could replace
both at once instead of making two trips, I dunno. =)

Thanks for your idea bout the switch, I had the same thoughts running
through my head about whether they did it right or something.

MW

> >The multi-function switch was replaced
>
[quoted text clipped - 5 lines]
>
> Dave S(Texas)

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lugnut - 20 Apr 2006 02:19 GMT

>I just cannot believe it..... Both bulbs burnt out at the same time. Went to
>the local parts store, bought new lamps, threw 'em in... bingo. I am
[quoted text clipped - 5 lines]
>
>MW

Maybe all that voltage that was able to pass thru a good MF
switch was more than the old darlin's could handle!

Lugnut

>> >The multi-function switch was replaced
>>
[quoted text clipped - 5 lines]
>>
>> Dave S(Texas)

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Whitelightning - 20 Apr 2006 06:41 GMT

> I just cannot believe it..... Both bulbs burnt out at the same time. Went to
> the local parts store, bought new lamps, threw 'em in... bingo. I am
[quoted text clipped - 5 lines]
>
> MW

I do believe you just learned O'Brians' Law.

Whitelightning

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Dave and Trudy - 20 Apr 2006 08:05 GMT

>I just cannot believe it..... Both bulbs burnt out at the same time. Went
>to
[quoted text clipped - 4 lines]
> Thanks for your idea bout the switch, I had the same thoughts running
> through my head about whether they did it right or something.

You said that you had the low beams on when you shut the truck down. OK, you
probably turned them off before you shut off the ignition but for both to
burn out at the same time indicates a power spike thru the bulbs. It may
have been a "one-time" event or it may be a symptom of other problems. If
the same thing happens again in the not too distant future, I would suspect
the switch that was recently replaced.

Dave D

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putt@webtv.net - 20 Apr 2006 14:38 GMT

>for both to burn out at the same time
> indicates a power spike thru the bulbs.

I'm curious about this: where/how in a 12v system could this 'power
spike' occur and why did it affect only the low-beam element in the
headlamps and no other electrical component of the vehicle?

> It may have been a "one-time" event or
> may be a symptom of other problems

LOL...good one!

Dave S(Texas)

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Dave and Trudy - 21 Apr 2006 08:25 GMT

> >for both to burn out at the same time
>> indicates a power spike thru the bulbs.
[quoted text clipped - 9 lines]
>
> Dave S(Texas)

If they were the only components energized thru the suspect switch and the
power spike was cause thereby, they would be the only component affected.
Quite simple when you use a little thought ,

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putt@webtv.net - 21 Apr 2006 15:33 GMT

>If they were the only components
> energized thru the suspect switch and
> the power spike was cause thereby,
> they would be the only component
> affected. Quite simple when you use a
> little thought

Dave/Trudy....your knowledge of electricity/systems is astounding. Your
'little thought' process is common to all DIY's....wtg

Dave S(Texas)

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RCE - 25 Apr 2006 11:07 GMT

>> >for both to burn out at the same time
>>> indicates a power spike thru the bulbs.
[quoted text clipped - 13 lines]
> power spike was cause thereby, they would be the only component affected.
> Quite simple when you use a little thought ,

Anything in the circuit that has some inductive reactance (coil, windings,
etc.) could cause a spike when the field collapses.

RCE

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RCE - 25 Apr 2006 11:04 GMT

>I just cannot believe it..... Both bulbs burnt out at the same time. Went
>to
> the local parts store, bought new lamps, threw 'em in... bingo. I am
> relieved, but bewildered. Maybe God graciously did this so I could replace
> both at once instead of making two trips, I dunno. =)

Heh. I should have read a few more posts.

Congrats! I thought I was the only one on earth that ever had that happen.

RCE

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RCE - 25 Apr 2006 11:02 GMT

> Drove to a restaurant with low-beams. Ate dinner. Started truck to go
> home.
[quoted text clipped - 11 lines]
>
> Mike W.

I had this problem many years ago on a '70 Plymouth. No low beams, but the
high beams worked fine. Spent a whole weekend in the driveway with a meter
tracing down the wiring, switches, etc., and could not find a wiring
problem.

Finally discovered the problem. Both low beam lights were burnt out. Could
never happen again in million years having both burn out at the same time,
but it did.

RCE

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