Both headlights out?
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Both headlights out?
We don't drive the 1973 F-100 360 but in the Summer each year, so we always have to make sure everything is working around this time so we can take it camping.
Last year both our headlights worked, and this year they both don't. All the other lights in the light switch work (compartment and parking lights).
What would cause both headlights to go out at once? I noticed there is no fuse in the fuse box for headlights, is it somewhere else like in the headlight switch?
Last year both our headlights worked, and this year they both don't. All the other lights in the light switch work (compartment and parking lights).
What would cause both headlights to go out at once? I noticed there is no fuse in the fuse box for headlights, is it somewhere else like in the headlight switch?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
There isn't a fuse for the headlights, instead a circuit breaker is built into the switch. With something this critical, you want to be able to have them come back on if you're stranded and can fix the problem on the side of the road.
I know this sounds obvious, but it's not impossible for both headlights to have gone out at the same time. It's worth your time to check for voltage at the headlight pigtails with a test light or multimeter.
I know this sounds obvious, but it's not impossible for both headlights to have gone out at the same time. It's worth your time to check for voltage at the headlight pigtails with a test light or multimeter.
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Postmaster
Joined: Dec 2008
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From: Southern Oregon Coast
Those switches have a tendency to get all kinds of crud in them and the contacts can get corroded which would cause a bad connection and, possibly, causing your lights to go out. The wiring diagram I just looked at shows the headlight circuit going from the headlight switch - through the dimmer switch - to the headlights. Since you said your courtesy and marker lights are working, I would continue to suspect the dimmer switch to be at fault.
If I'm reading this diagram correctly - at the dimmer switch, the red/yellow wire goes to the headlight switch, the green/black wire is the high beam, and the red/black wire is the low beam. Look for frayed wire and possible shorts if you haven't already done so.
Edit: Or... do what fmc400 suggested above, I forgot about the circuit breaker...
If I'm reading this diagram correctly - at the dimmer switch, the red/yellow wire goes to the headlight switch, the green/black wire is the high beam, and the red/black wire is the low beam. Look for frayed wire and possible shorts if you haven't already done so.
Edit: Or... do what fmc400 suggested above, I forgot about the circuit breaker...
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Alright, tomorrow I'll pull out the ignition switch (do I need to pull it all the way out?) and check the circuit breaker. If it looks bad, I'll replace it. Otherwise, I'll test the headlight voltage and possibly then TRY to find a problem with the dimmer switch.
Thank you guys
Thank you guys
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Don't do anything with the ignition switch - it's all in the headlight switch.
Test the voltage on the sockets before you pull anything apart. Always start with the most obvious stuff. Anytime you're diagnosing an electrical issue (or really any issue), always make informed decisions based on quantitative diagnosis - not "if it looks bad."
Test the voltage on the sockets before you pull anything apart. Always start with the most obvious stuff. Anytime you're diagnosing an electrical issue (or really any issue), always make informed decisions based on quantitative diagnosis - not "if it looks bad."
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Don't do anything with the ignition switch - it's all in the headlight switch.
Test the voltage on the sockets before you pull anything apart. Always start with the most obvious stuff. Anytime you're diagnosing an electrical issue (or really any issue), always make informed decisions based on quantitative diagnosis - not "if it looks bad."
Test the voltage on the sockets before you pull anything apart. Always start with the most obvious stuff. Anytime you're diagnosing an electrical issue (or really any issue), always make informed decisions based on quantitative diagnosis - not "if it looks bad."
Alright, I'll test the headlight sockets. Is there exposed metal there to test or do I have to pull them out?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Just pull the connector off the back of the headlight, and push your meter probes down into the socket with the headlight switch on. One of the tabs is ground, one is high beam and one is low beam. I can't remember which color is which, but a wiring diagram on Autozone's website would have that information.
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I don't know if this could be related, but our instrument panel bulbs are all out
I just tested the bulbs and they work fine... no voltage getting to them though.
Pulled out the headlight switch. How can I test it?
I just tested the bulbs and they work fine... no voltage getting to them though.
Pulled out the headlight switch. How can I test it?
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Alright, it works again after replacing the headlight switch and dimmer switch 
Thank you everyone!
Thank you everyone!
Last edited by GreatWalrus; Jul 12, 2009 at 05:38 PM. Reason: keep calling it an ignition switch LOL
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