Headlights only work in high beams
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Mountain Pass
Joined: Sep 2020
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Headlights only work in high beams
Hey gang my headlights only work in high beam using the floor switch and I was wondering if anybody’s had this issue or if it’s an issue at all because the high beams seem pretty mellow.
Lead Driver
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Probably the floor switch went bad. Could also be simultaneous or nearly so low elements went bad? Not likely.
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Could be more common than you think for both bulbs to have the low beam filaments burned out. For all we know, one could have been burned out for some time but it wasn’t noticed. When was the last time you had checked that both had been working? Then when the second bulb failed, maybe months later, you finally notice and think something funky is happening.
Same thing happened to my boss, and he is a top notch electrical troubleshooter. He gets to work one morning and says both low beams were dead. He starts pulling up wiring diagrams, researching light control modules (it was a newer car), and so on, looking for a common failure point. I asked when was the last time he had checked his headlights, but he thought it couldn’t be two bad bulbs. The next day he had to sheepishly buy me lunch (I ordered steak) because that was it.
Before trying any parts, I’d do some basic power checks with a voltmeter at the bulb sockets. Or just try one bulb and see what happens. If it works, buy a second bulb for the other side. If no joy after trying this new bulb on both sides, it’s probably a bad dimmer switch. Set the new bulb aside as a spare, because you will need it one day.
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From: Angier, NC
Dave ----
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Mountain Pass
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Thanks for all the feedback first. Also not to my knowledge. The truck sat for 10 years so unlikely. Will someone include a link to the new harness? It’s an 86. To reiterate I’m able to activate the lights with the dash **** and if I click engage the floor switch. It will go off and on. I’ll test with a voltmeter to see the power. I’d prefer to not do an unnecessary upgrade unless its far superior and simplifys wires.
Lead Driver
Joined: Apr 2002
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Thanks for all the feedback first. Also not to my knowledge. The truck sat for 10 years so unlikely. Will someone include a link to the new harness? It’s an 86. To reiterate I’m able to activate the lights with the dash **** and if I click engage the floor switch. It will go off and on. I’ll test with a voltmeter to see the power. I’d prefer to not do an unnecessary upgrade unless its far superior and simplifys wires.
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
You can find them on Ebay, Amazon, LMC and others.
Hate LMC on line lay out now!
http://www.lmctruck.com/1980-96-ford...dlight-harness
I have one installed in my truck and love it also have a 2nd one for a car project to use it on.
I bought both years ago even before I had the truck.
Dave ----
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Thanks for all the feedback first. Also not to my knowledge. The truck sat for 10 years so unlikely. Will someone include a link to the new harness? It’s an 86. To reiterate I’m able to activate the lights with the dash **** and if I click engage the floor switch. It will go off and on. I’ll test with a voltmeter to see the power. I’d prefer to not do an unnecessary upgrade unless its far superior and simplifys wires.
FTE Legend
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From: Angier, NC
Lights will be brighter, but definitely adds complication. It would be easiest to test with your meter at the floor switch itself. I would imagine once you get the switch off the problem will be apparent without the meter, the switch leads a hard life down there in the floorboard.
I say it is 50/50 on where to test at.
Me being an old fart and its getting harder getting under the dash / floor were the dimmer switch is ( I was just there doing some wiring at the fuse box) I would pick at the head light.
Pull the plug at the light, turn the head lights on and test with meter or test light.
Just remember of the 3 connections 1 is high beam, 1 low beam, 1 ground.
I would ground the test light / meter and with lights on low test the 3 connections, 1 should have power and 1 a ground.
Flip to high and test again, the one that had power will not now and 1 other should have power.
If you find you now have 2 with out power, you know the one that had power on low, then the dimmer switch is bad and can test there if you want.
At the dimmer you have 3 wires, power in when the head lights are on.
1 wire id low and the other high. The switch switches between the other 2 wires.
You will have power out on 1 for high and when switched no power on the 2 out going wires = bad switch.
Think the hardest part of testing dimmer switch is needing to pull back the carpet besides getting down and back up from there - remember old fart here LOL
Dave ----
Lead Driver
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Yes lights will be brighter!
I say it is 50/50 on where to test at.
Me being an old fart and its getting harder getting under the dash / floor were the dimmer switch is ( I was just there doing some wiring at the fuse box) I would pick at the head light.
Pull the plug at the light, turn the head lights on and test with meter or test light.
Just remember of the 3 connections 1 is high beam, 1 low beam, 1 ground.
I would ground the test light / meter and with lights on low test the 3 connections, 1 should have power and 1 a ground.
Flip to high and test again, the one that had power will not now and 1 other should have power.
If you find you now have 2 with out power, you know the one that had power on low, then the dimmer switch is bad and can test there if you want.
At the dimmer you have 3 wires, power in when the head lights are on.
1 wire id low and the other high. The switch switches between the other 2 wires.
You will have power out on 1 for high and when switched no power on the 2 out going wires = bad switch.
Think the hardest part of testing dimmer switch is needing to pull back the carpet besides getting down and back up from there - remember old fart here LOL
Dave ----
I say it is 50/50 on where to test at.
Me being an old fart and its getting harder getting under the dash / floor were the dimmer switch is ( I was just there doing some wiring at the fuse box) I would pick at the head light.
Pull the plug at the light, turn the head lights on and test with meter or test light.
Just remember of the 3 connections 1 is high beam, 1 low beam, 1 ground.
I would ground the test light / meter and with lights on low test the 3 connections, 1 should have power and 1 a ground.
Flip to high and test again, the one that had power will not now and 1 other should have power.
If you find you now have 2 with out power, you know the one that had power on low, then the dimmer switch is bad and can test there if you want.
At the dimmer you have 3 wires, power in when the head lights are on.
1 wire id low and the other high. The switch switches between the other 2 wires.
You will have power out on 1 for high and when switched no power on the 2 out going wires = bad switch.
Think the hardest part of testing dimmer switch is needing to pull back the carpet besides getting down and back up from there - remember old fart here LOL
Dave ----
And yeah you only need to test the low if you can remember which one it is. I knew if I said test all three in both positions the OP would hit paydirt and figure it out all three.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Because I dint know what one would be low, high or ground I would be testing all 3 LOL
Yea about pulling the kick panel to move carpet.
So testing at light would be easier but may still need to deal with that panel & carpet
Dave ----
Yea about pulling the kick panel to move carpet.
So testing at light would be easier but may still need to deal with that panel & carpet
Dave ----
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Tuned
Joined: Apr 2008
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Well the upgrade does add some complexity but its not bad. If I can do it, anyone can do it. Not only will the harness upgrade make your halogen lights brighter, I consider it a safety upgrade as well. Stock, if your dimmer switch takes a crap on you, it could kill your headlights all together which to me equals bad. Because the only time you're going to know if that switch goes bad, is when you are using it lol. With the harness upgrade, the lights get power directly from battery through some relays so if the switch goes bad, you will still have headlights. Yes, relays can go bad too but there are two of them - one for brights and one for dim. So that's my 2 cents. With all that being said, I would NOT do the harness upgrade until you figure out the current problem first.
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