Headlights cause power drop
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
Headlights cause power drop
Hey all, I recently got my factory (84) headlight switch to work (when turning it far left, to engage the bed and courtesy lights), and now I'm losing voltage down to about 4v everywhere that is an ACC hot with the headlights on. The headlights and running lights operate fine with no problems, turn the headlights off and everything goes back up to 12V. Is there a grounding issue with my headlight switch or do I possibly have a bad ground somewhere else? I doubt the grounding on the harness considering this wasn't happening when the switch wouldn't turn on the bed light. I will be replacing the switch here soon. I just wanted to see if anyone else has ever had this problem.
Thanks.
Thanks.
Thread Starter
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
There is 100% ground to everything. I just re-ran the ground like it was from the factory but cleaned everything up and made it waterproof to prevent rust on it but I can touch anywhere on the frame or body and get a constant solid ground. If it has one, it's like the ground in the switch is shorting out.
Thread Starter
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
Upon messing with the **** if I turn it to a certain point I can get my 11.8V back on my stereo ACC wire but it’s super finicky
Lead Driver
Joined: Nov 2013
Posts: 7,162
Likes: 1,169
Not sure what is happening that adjusting the panel lighting (turning the headlight ****) would affect the ACC circuit powering the radio.
Maybe some non-stock wiring? Power to the radio should be via fuse #11. Turn the key to ACC, turn on the radio, and then pull fuse #11. The radio should stop playing.
After confirming fuse #11 powers the radio, run the following test. Don't be scared, it's all simple voltage measurements recorded at the fuse panel. For your situation, measure between fuses #1 and #11.
https://www.ford-trucks.com/forums/1...on-switch.html
If good, your headlight switch is probably the culprit. Still unsure how one circuit is affecting a seemingly unrelated circuit, but who knows. And you did report you could fiddle with the **** and all returned to normal.
Maybe some non-stock wiring? Power to the radio should be via fuse #11. Turn the key to ACC, turn on the radio, and then pull fuse #11. The radio should stop playing.
After confirming fuse #11 powers the radio, run the following test. Don't be scared, it's all simple voltage measurements recorded at the fuse panel. For your situation, measure between fuses #1 and #11.
https://www.ford-trucks.com/forums/1...on-switch.html
If good, your headlight switch is probably the culprit. Still unsure how one circuit is affecting a seemingly unrelated circuit, but who knows. And you did report you could fiddle with the **** and all returned to normal.
Moderator
Joined: Jan 2001
Posts: 56,977
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From: Virginia
Sounds like the radio is wired wrong, especially if it's not factory. The lightblue/red wire is for illumination. There is a special wire on all radios for this one certain wire to light the dial, or on a modern radio to dim the digital display when the dash lights come on. Most modern radios, and the Ford digital radios, have two power sources to the radio. One is battery power for the memory, and the other is key on power for the rest of the radio.
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
Sounds like the radio is wired wrong, especially if it's not factory. The lightblue/red wire is for illumination. There is a special wire on all radios for this one certain wire to light the dial, or on a modern radio to dim the digital display when the dash lights come on. Most modern radios, and the Ford digital radios, have two power sources to the radio. One is battery power for the memory, and the other is key on power for the rest of the radio.
I have put an aftermarket radio in but I hooked every wire up exactly like the diagram shows and everything is color coated. The only thing is the cassette radio player I took out did not have a constant hot. I just ran a wire directly from the battery and hooked it up that way. When the truck is off that wire shows 11v and the ACC is zero. Turn the ACC on and both show 11v. However you turn the headlights or running lights on it drops to 4v on the direct wire from battery and like .4v dead on the ACC. When testing the two wires that fed the old radio I checked each with key off and ACC and used the one that powered up as the ACC source for radio. Again everything works perfectly wether driving or at idle but you turn the headlights on down goes power for radio.
Fuse 11 does maintain constant power with headlights on and does cut the radio when pulled
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
I was wondering if he was measuring the "dash light" wire to the radio as pointed out by Karl and DaveF?
Have never had a need to measure the dash light volts but what I gather that is what you are doing and the head light switch might need to be replaced if it is cutting in & out?
I am running green LED bulbs in the dash with no color covers and it looks like factory color. For the waring light at the top I run red LED for the seat belt and clear / white for the others.
Dave ----
Have never had a need to measure the dash light volts but what I gather that is what you are doing and the head light switch might need to be replaced if it is cutting in & out?
I am running green LED bulbs in the dash with no color covers and it looks like factory color. For the waring light at the top I run red LED for the seat belt and clear / white for the others.
Dave ----
FTE Legend
Joined: Nov 2015
Posts: 30,876
Likes: 4,116
From: Angier, NC
Oh being we are talking about head lights are you running the head light relays?
It takes the load off the switch as it is used only to trigger the relays.
It also makes the head lights brighter as they not get a full 12 volts from the battery.
The factory set up runs from the battery to the switch to the high / low dimmer and out to the head light bulbs all through old wiring.
LMC, Ebay, think Amazon sells the kit and it is plug n play.
Best thing I have done to my truck.
Dave -----
It takes the load off the switch as it is used only to trigger the relays.
It also makes the head lights brighter as they not get a full 12 volts from the battery.
The factory set up runs from the battery to the switch to the high / low dimmer and out to the head light bulbs all through old wiring.
LMC, Ebay, think Amazon sells the kit and it is plug n play.
Best thing I have done to my truck.
Dave -----
Thread Starter
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
Oh being we are talking about head lights are you running the head light relays?
It takes the load off the switch as it is used only to trigger the relays.
It also makes the head lights brighter as they not get a full 12 volts from the battery.
The factory set up runs from the battery to the switch to the high / low dimmer and out to the head light bulbs all through old wiring.
LMC, Ebay, think Amazon sells the kit and it is plug n play.
Best thing I have done to my truck.
Dave -----
It takes the load off the switch as it is used only to trigger the relays.
It also makes the head lights brighter as they not get a full 12 volts from the battery.
The factory set up runs from the battery to the switch to the high / low dimmer and out to the head light bulbs all through old wiring.
LMC, Ebay, think Amazon sells the kit and it is plug n play.
Best thing I have done to my truck.
Dave -----
No I am not I will definitely have to look into those. I’m most likely looking at redoing a majority of my grounds due to age and rust so that will probably help out a lot too. If I plan to upgrade to LEDs would the relays be a waste of time or would that just be a plus with the LEDs?
Thread Starter
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5th Wheeling
Joined: Feb 2023
Posts: 46
Likes: 3
From: Fort Hood
Did notice it was starting to drop hooked up my tester and it said to replace battery good thing it’s under warranty still but it’s not helping me with my problem hooked up to a beefy charger. I even ran a wire to what I believe was the pcv connector plug that powers on with ACC and it even losses power when hooked to that with the headlights coming on.
FTE Legend
Joined: Nov 2015
Posts: 30,876
Likes: 4,116
From: Angier, NC
No I am not I will definitely have to look into those. I’m most likely looking at redoing a majority of my grounds due to age and rust so that will probably help out a lot too. If I plan to upgrade to LEDs would the relays be a waste of time or would that just be a plus with the LEDs?
It also sounds like you are doing this volt measuring with the motor off?
Start and let it run a bit to recharge the battery then do your measuring.
You never want to check things like voltage when the motor should be running.
You dont run the head light with out the motor running do you?
Dave ----
Lead Driver
Joined: Nov 2013
Posts: 7,162
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I've got a theory of what may be happening, but need some more details, please.
Did you run the voltage drop test of the ignition switch? See post #6 above.
Does your truck have an ammeter or a battery idiot light? There are some differences in the wiring, so need to know which version you have.
You mentioned the voltage drops on certain circuits when the headlights are on. Let's continue using fuse #11 as our reference point. What happens when you only pull the headlight switch out to the first click, for parking lights only and no headlights. Does the problem still exist? Or is it only when the **** is pulled all the way out for headlights?
As far as converting to the relay system for the headlights, this is not a bad idea but I'd suggest holding off for now. Find and fix the problem before making any further changes. Even if you did the conversion and all seemed okay for now, the original problem is still there and could further degrade and come back to bite you down the road.
Did you run the voltage drop test of the ignition switch? See post #6 above.
Does your truck have an ammeter or a battery idiot light? There are some differences in the wiring, so need to know which version you have.
You mentioned the voltage drops on certain circuits when the headlights are on. Let's continue using fuse #11 as our reference point. What happens when you only pull the headlight switch out to the first click, for parking lights only and no headlights. Does the problem still exist? Or is it only when the **** is pulled all the way out for headlights?
As far as converting to the relay system for the headlights, this is not a bad idea but I'd suggest holding off for now. Find and fix the problem before making any further changes. Even if you did the conversion and all seemed okay for now, the original problem is still there and could further degrade and come back to bite you down the road.