Headlight dimming and flickering
Thread Starter
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Freshman User
Joined: May 2015
Posts: 25
Likes: 0
Headlight dimming and flickering
Hey guys...still trying to track down the following electrical issue, 74 f250:
First off, the truck has a new painless harness, a 3g alt upgrade and a pretty hefty stereo in it. I don't know if any of these are the issue, but possibly.
On startup, all the of the electrical works fine. 14.2 at the battery with all accessories running. As long as I sit at idle, everything is A-0K.
When I pull away, the headlights will start to dim and sometimes completely go off for just a split second. While this happens, the voltmeter is dancing all over the place, sometimes as low as 10.
The number at the battery seems to indicate an OK charging system, so I'm thinking a wiring issue in the headlight circuit, but here's the thing....after about a minute of driving everything is fine....voltmeter is steady between 13-14 and the headlights are strong and solid. Based on that, I would think voltage regulator, but I've had the same issue with two different 3g alternators.
Basically I'm lost at this point...any help would be greatly appreciated.
First off, the truck has a new painless harness, a 3g alt upgrade and a pretty hefty stereo in it. I don't know if any of these are the issue, but possibly.
On startup, all the of the electrical works fine. 14.2 at the battery with all accessories running. As long as I sit at idle, everything is A-0K.
When I pull away, the headlights will start to dim and sometimes completely go off for just a split second. While this happens, the voltmeter is dancing all over the place, sometimes as low as 10.
The number at the battery seems to indicate an OK charging system, so I'm thinking a wiring issue in the headlight circuit, but here's the thing....after about a minute of driving everything is fine....voltmeter is steady between 13-14 and the headlights are strong and solid. Based on that, I would think voltage regulator, but I've had the same issue with two different 3g alternators.
Basically I'm lost at this point...any help would be greatly appreciated.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
Install a headlight relay system and the headlight issue should go away.... unless the headlight switch is truly on its last legs.
Btw, inspect the headlight and high beam switches/wiring and connectors too.
Btw, inspect the headlight and high beam switches/wiring and connectors too.
Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
+1 on the relay system...instead of relying on the harness and switch to carry all the current to the headlights, you put in a coupel of new, short heavy gauge wires to carry the load. I would estimate an easy 50% increase in headlight brightness when I did mine. Even though you put in new harness, you are still running current through the old headlight and dimmer switches. I suspect one of them has an iffy contact which starts with a bad contact, and the intermittent contact heats up after a few seconds to the point where it is making good contact. Just a theory.... One other thing to check - when you installed the new harness did you actually clean the grounds or just install the wires to the old screws? If the latter, a little sandpaper at the contact points to shine things up would also improve the circuit.
Thread Starter
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Freshman User
Joined: May 2015
Posts: 25
Likes: 0
I got clean grounds on all my new wiring. Tonight I'm going to replace the main ground from battery to block and clean up my block to frame ground to see if that helps.
As a side note, I noticed my front marker lights are not illuminating now, so I'm sure that's related. I'll keep you posted, but any other ideas are appreciated.
As a side note, I noticed my front marker lights are not illuminating now, so I'm sure that's related. I'll keep you posted, but any other ideas are appreciated.
Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
Fix
Hey guys...still trying to track down the following electrical issue, 74 f250:
First off, the truck has a new painless harness, a 3g alt upgrade and a pretty hefty stereo in it. I don't know if any of these are the issue, but possibly.
On startup, all the of the electrical works fine. 14.2 at the battery with all accessories running. As long as I sit at idle, everything is A-0K.
When I pull away, the headlights will start to dim and sometimes completely go off for just a split second. While this happens, the voltmeter is dancing all over the place, sometimes as low as 10.
The number at the battery seems to indicate an OK charging system, so I'm thinking a wiring issue in the headlight circuit, but here's the thing....after about a minute of driving everything is fine....voltmeter is steady between 13-14 and the headlights are strong and solid. Based on that, I would think voltage regulator, but I've had the same issue with two different 3g alternators.
Basically I'm lost at this point...any help would be greatly appreciated.
First off, the truck has a new painless harness, a 3g alt upgrade and a pretty hefty stereo in it. I don't know if any of these are the issue, but possibly.
On startup, all the of the electrical works fine. 14.2 at the battery with all accessories running. As long as I sit at idle, everything is A-0K.
When I pull away, the headlights will start to dim and sometimes completely go off for just a split second. While this happens, the voltmeter is dancing all over the place, sometimes as low as 10.
The number at the battery seems to indicate an OK charging system, so I'm thinking a wiring issue in the headlight circuit, but here's the thing....after about a minute of driving everything is fine....voltmeter is steady between 13-14 and the headlights are strong and solid. Based on that, I would think voltage regulator, but I've had the same issue with two different 3g alternators.
Basically I'm lost at this point...any help would be greatly appreciated.
I got clean grounds on all my new wiring. Tonight I'm going to replace the main ground from battery to block and clean up my block to frame ground to see if that helps.
As a side note, I noticed my front marker lights are not illuminating now, so I'm sure that's related. I'll keep you posted, but any other ideas are appreciated.
As a side note, I noticed my front marker lights are not illuminating now, so I'm sure that's related. I'll keep you posted, but any other ideas are appreciated.
Thread Starter
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Freshman User
Joined: May 2015
Posts: 25
Likes: 0
The relay fixed mine. At least I'm pretty sure it did. I also cleaned up a block to frame ground and added a ground from the inner fender to the underside of the hood, which is supposed to be there...but mine wasn't. So, one of those things cleared it up.
Good luck on yours!
Good luck on yours!
Trending Topics
Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
The relay fixed mine. At least I'm pretty sure it did. I also cleaned up a block to frame ground and added a ground from the inner fender to the underside of the hood, which is supposed to be there...but mine wasn't. So, one of those things cleared it up.
Good luck on yours!
Good luck on yours!
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Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
Fingers crossed
Well I just finished installing the relay harness...Holy cow are those lights bright! True test will be tomorrow morning at 6:00 to see if they still flicker. I took it for a spin and I still see the voltage dropping a bit and I might have heard a little belt squeal, so i think i will change the belt. I have a hard time tightening it because i have to tug on the alternator with one hand and tighten the bolts with the other. My radio is cutting out when I accelerate or hit a bump. It doesnt lose its presets or anything, just powers off then back on. I may pull the dash and check it out or remove it altogether. Do they still make the headliner with speakers in it?
Laughing Gas
Joined: Jun 2016
Posts: 855
Likes: 56
From: Des Moines, Washington
I think I've seen a headliner or maybe a thing that fits along the top of the windshield that has a radio mount and speakers but since I can't see stop lights due to the height of the windshield, I'm sticking with the radio shack cheapo installed in the late 90's
If the boss on the alternator that the curved bracket is bolted to is a biggish square lug, I usually put a 10" or 12" Crescent wrench on it and pull hard. But not too hard. I look for about 1/2" deflection in the middle of the longest run when I push hard with one finger.
Michael
Michael
If the boss on the alternator that the curved bracket is bolted to is a biggish square lug, I usually put a 10" or 12" Crescent wrench on it and pull hard. But not too hard. I look for about 1/2" deflection in the middle of the longest run when I push hard with one finger.
Michael
Michael
Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
I think I've seen a headliner or maybe a thing that fits along the top of the windshield that has a radio mount and speakers but since I can't see stop lights due to the height of the windshield, I'm sticking with the radio shack cheapo installed in the late 90's
If the boss on the alternator that the curved bracket is bolted to is a biggish square lug, I usually put a 10" or 12" Crescent wrench on it and pull hard. But not too hard. I look for about 1/2" deflection in the middle of the longest run when I push hard with one finger.
Michael
Michael
If the boss on the alternator that the curved bracket is bolted to is a biggish square lug, I usually put a 10" or 12" Crescent wrench on it and pull hard. But not too hard. I look for about 1/2" deflection in the middle of the longest run when I push hard with one finger.
Michael
Michael
Laughing Gas
Joined: Jun 2016
Posts: 855
Likes: 56
From: Des Moines, Washington
You are welcome.
Just don't pull so hard you break the alternator.
I have the LMC cluster lens. It's OK but the mold maker put the ejector pins just left and right of center on the speedo section. Drives me crazy to see 2 1/4" circles in the middle of my otherwise perfect speedo!
The radio may be as simple as a poor ground. If the installer counted on the volume and tune shaft nuts making a good connection, they chose badly. Same goes for using the antenna as a ground.
Michael
Just don't pull so hard you break the alternator.
I have the LMC cluster lens. It's OK but the mold maker put the ejector pins just left and right of center on the speedo section. Drives me crazy to see 2 1/4" circles in the middle of my otherwise perfect speedo!
The radio may be as simple as a poor ground. If the installer counted on the volume and tune shaft nuts making a good connection, they chose badly. Same goes for using the antenna as a ground.
Michael
Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
You are welcome.
Just don't pull so hard you break the alternator.
I have the LMC cluster lens. It's OK but the mold maker put the ejector pins just left and right of center on the speedo section. Drives me crazy to see 2 1/4" circles in the middle of my otherwise perfect speedo!
The radio may be as simple as a poor ground. If the installer counted on the volume and tune shaft nuts making a good connection, they chose badly. Same goes for using the antenna as a ground.
Michael
Just don't pull so hard you break the alternator.
I have the LMC cluster lens. It's OK but the mold maker put the ejector pins just left and right of center on the speedo section. Drives me crazy to see 2 1/4" circles in the middle of my otherwise perfect speedo!
The radio may be as simple as a poor ground. If the installer counted on the volume and tune shaft nuts making a good connection, they chose badly. Same goes for using the antenna as a ground.
Michael
Senior User
Joined: Feb 2018
Posts: 108
Likes: 1
Well guys...Still flickering. But since I have a working voltmeter I noticed something interesting. As I was pulling into the gas station this morning, there was a slight incline in the pavement. When I hit it, voltage dropped. As I pulled back into the roadway, same thing...Roadway dipped, so did my voltage. Thinking my body grounds are shot so I am going to do some serious grounding tonight. Block to frame, frame to body, firewall to hood. Whatcha think?