Headlight wiring questions
Thread Starter
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Trailering
Joined: Oct 2022
Posts: 20
Likes: 2
From: Redwood City, CA
Headlight wiring questions
Howdy everybody - been searching and reading and trying to get up to speed on my recently inherited 66 F-100 flareside I have a horrible track record for buying things that end up not fitting or not working as intended. I'm trying to limit that as much as possible on this truck.
I grabbed some "plug and play" LED headlights and, as you may have guessed, they plugged but did not play. At all. Previous posts suggested a polarity problem, so I grabbed one of these and now I have high beams, but no low beams. (I see now that I should have bought http://www.holley.com/products/electrical/led_lighting/retrobright/parts/H820)
I was on my way to order the wiring harness from Tom's but thought I'd ask the group if there was anything obvious I'm overlooking? Too little power? Too much?
thanks in advance
I grabbed some "plug and play" LED headlights and, as you may have guessed, they plugged but did not play. At all. Previous posts suggested a polarity problem, so I grabbed one of these and now I have high beams, but no low beams. (I see now that I should have bought http://www.holley.com/products/electrical/led_lighting/retrobright/parts/H820)
I was on my way to order the wiring harness from Tom's but thought I'd ask the group if there was anything obvious I'm overlooking? Too little power? Too much?
thanks in advance
Last edited by dUb100; Oct 28, 2022 at 11:42 AM.
Cargo Master
Joined: Apr 2003
Posts: 2,389
Likes: 58
Maybe the LEDs are defective. It is even stated that they are a replacement for the sealed beams so if the sealed beams work, the leds should work as supplied out of the box.
I know it will probably be a waste of time but have you tried contacting Holley tech support?
Make sure the voltage is adequate at the plug. LEDs simply will not turn on if voltage is below a certain threshold. That exact number can vary depending on the design of the lights. Where voltage may be good enough for an incandescent bulb to glow, at the very least, an LED may simply not turn on.
I know it will probably be a waste of time but have you tried contacting Holley tech support?
Make sure the voltage is adequate at the plug. LEDs simply will not turn on if voltage is below a certain threshold. That exact number can vary depending on the design of the lights. Where voltage may be good enough for an incandescent bulb to glow, at the very least, an LED may simply not turn on.
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Thread Starter
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Trailering
Joined: Oct 2022
Posts: 20
Likes: 2
From: Redwood City, CA
Good point. Time to break out the voltmeter
I did try to contact Holley but got radio silence thus far
I did try to contact Holley but got radio silence thus far
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Thread Starter
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Trailering
Joined: Oct 2022
Posts: 20
Likes: 2
From: Redwood City, CA
At headlight on high - 11v
At headlight on low - 0.3v
At foot switch on high - 11v
At foot switch on low- 11v
Old headlight no longer functions on low, so I may have caused new problems.
what lies between the foot switch and the headlight?
At headlight on low - 0.3v
At foot switch on high - 11v
At foot switch on low- 11v
Old headlight no longer functions on low, so I may have caused new problems.
what lies between the foot switch and the headlight?
FTE Legend
Joined: Nov 2015
Posts: 30,898
Likes: 4,120
From: Angier, NC
Well one of the first things you should have done before the LED bulbs was the head light relay kit with Halogen sealed bulbs.
The relays do 2 things
1- takes the load off you head light switch as it is now used to work the relays.
2- the head lights now get full voltage and that makes them brighter.
When you checked voltage and got 11 volts what was the battery volts running and off?
Bet is was more then 11 volts as that would not be enough to start the motor.
You can get the relay kit from LMC and Ebay, think Amazon and I am sure others.
What is nice is it is plug n play no cutting of wires.
I run the LMC kit on my 81 F100 flare side and had a relay stop working because I washed the engine bay and got water in it.
Because I wanted to use the truck for work at 2am I just unplugged the relays and plug the trucks head light harness plugs back in till I could replace the relay.
Dave ----
The relays do 2 things
1- takes the load off you head light switch as it is now used to work the relays.
2- the head lights now get full voltage and that makes them brighter.
When you checked voltage and got 11 volts what was the battery volts running and off?
Bet is was more then 11 volts as that would not be enough to start the motor.
You can get the relay kit from LMC and Ebay, think Amazon and I am sure others.
What is nice is it is plug n play no cutting of wires.
I run the LMC kit on my 81 F100 flare side and had a relay stop working because I washed the engine bay and got water in it.
Because I wanted to use the truck for work at 2am I just unplugged the relays and plug the trucks head light harness plugs back in till I could replace the relay.
Dave ----
Thread Starter
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Trailering
Joined: Oct 2022
Posts: 20
Likes: 2
From: Redwood City, CA
Thanks for everyone's feedback.
Meanwhile, my theme song continues to play:
- I bought a harness + relays from Tom's Offroad and plugged everything in. Still only have high beams.
- Checked the voltage at the plug and there is no power when on the low beams
- I tried a new dimmer switch and had the same result.
- Swapped the relays on the new harness just to make sure all was good. It is.
- Now that power is coming straight from the battery, what prevents that power from getting to the low beams?
Meanwhile, my theme song continues to play:
FTE Legend
Joined: Nov 2015
Posts: 30,898
Likes: 4,120
From: Angier, NC
At the dimmer switch on the floor there should be 3 wires.
1 is power when the head lights are turned on.
The switch then sends that power out on 1 or the other wires.
1 of the wires being low beam the other high beam.
I would look over the plug at the floor switch real good for corrosion or broken wire.
I am sure you can get that pig tail so might be easier to just replace it.
You can also jump from the power wire to the others with a jumper wire for testing but I would say that plug at the switch is bad.
Dave ----
1 is power when the head lights are turned on.
The switch then sends that power out on 1 or the other wires.
1 of the wires being low beam the other high beam.
I would look over the plug at the floor switch real good for corrosion or broken wire.
I am sure you can get that pig tail so might be easier to just replace it.
You can also jump from the power wire to the others with a jumper wire for testing but I would say that plug at the switch is bad.
Dave ----
Thread Starter
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Trailering
Joined: Oct 2022
Posts: 20
Likes: 2
From: Redwood City, CA
Thanks everyone
At the dimmer switch, I saw:
11.5V coming in (top connector)
Low beam - 11.5V at left connector, 6V at right connector
High beam - 3V at left connector, 11.5V at right connector
Is it normal to have voltage at the non-selected connector?
At the dimmer switch, I saw:
11.5V coming in (top connector)
Low beam - 11.5V at left connector, 6V at right connector
High beam - 3V at left connector, 11.5V at right connector
Is it normal to have voltage at the non-selected connector?