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Pulsing lights or flicker

428kidd

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Mar 7, 2022
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45
So any of y'all have a flicker or a pulse of your head lights at night? I have a new Centech harness , new parts store alternator and voltage regulator. I'm thinking it's the regulator but uncertain. Anyone help me out on what to replace or to do? The only issue I have ever noticed is that the charge hand kinda bounces around. Thanks Lance
 

DirtDonk

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Is there a small ground wire connected between the alternator case and the regulator mounting bolts on the body?
Is the engine painted and/or rusty where the alternator mounts to the engine block, or perhaps the threaded holes rusty?
Which wire are connected to the regulator and which wires are connected to the alternator? Which colors in other words?
Is the body clean where the regulator mounts to it? Is there any fresh paint underneath?
Did you do the install or did you have it done?

Parts store regulators and alternators do not have the best reputation these days. Could be something wrong with either of them.
I’m not sure if a full fielding test would indicate anything here, but it’s not hard to do and could be worth a try just to see what happens.
If you’re not sure what that is let us know and we can walk you through it.
 
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428kidd

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I dont recall a ground from the case to the regulator, but will check. I will add that if the vechile is not running there is not pulsing or anything. Once it is running thats when the problem starts. It also is not in just the headlights but all the lights. I installed the wiring harness just as the instructions how ever poor said to do so. Thanks guys!!
 

EPB72

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Do you have a multimeter? have you had the battery tested ?{probally not the issue but good to rule it out } recheck connections /grounds,,,
Check the charging system,,put a volt meter across the battery terminals and see what you get any fluctuations , high/low voltage?? you can also switch the meter to AC and see if you have any stray ac voltage .normal about .33 volts or less.....maybe put a test light across the battery to see if you get the flicker there as well...

also while it's flickering try disconnecting the voltage regulayor plug and see if that stops it ,taking tht charging system out of the picture...?
 
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428kidd

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Mar 7, 2022
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No stock lights no relays or led. I do have volt meter, the battery is 3 months old maybe , brand new basically. I can check that maybe this evening depending on when I get home.
 

Broncobowsher

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The flicker is an unstable alternator output. That is what the added ground wire Paul mentioned can sometimes help with. Good solid grounds. The regulator is looking at the ground on the regulator body, attached to the bronco body and trying to control alternator output. Alternator output is grounded to the engine block, a slightly different ground. The steel body isn't the greatest ground, add in years of paint, rust, oxidation of non-iron metals, wiring changes that may have happened...
On top of that the old voltage regulator design is mechanical. Not the most stable. When I did EFI on my F250 the Sniper was tripping out with under and over voltage alarms all the time. Nothing sustained, just flickers. Like how the lights flicker. My fix was a little 90A 3G alternator. More than enough output, but not so much that the single V-belt squealed like the 130A version does. It had a nice internal regulator. Output was much more stable, no flicker, no under/over voltage alarms on the EFI.
 

Rustytruck

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Feb 24, 2002
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10,875
Do you have the tall voltage regulator or the short electronic voltage regulator. the newer design electronic regulator works much better than the old mechanical one. if you must use the stock style alternator then I would step up to the motorcraft electronic regulator. best bet upgrade to the 4G alternator it puts out more power at Idle speed. the stock one was never enough charge mostly kept up until you had the headlights on and the wipers going then the lights would pulse it idle.

make sure you have good grounds. ground from negative of battery to the body tub and to the engine block I ground to the alternator case and the bottom of the voltage regulator and the mounting bolts for the starter solenoid. additional grounds between the tranny ir intake to the firewall doesnt hurt there are grounds for the headlights to the core support.



 
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428kidd

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Thanks guys, it has the short regulator, I'm going to get another one from a 78 Granada and replace the one I have. Clean the mounting area and check the grounds. I will get back asap. Thanks Lance
 

DirtDonk

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Before you do any of that add a ground wire between the alternator case and the voltage regulator bolt.

That is one of the most basic components of this charging system and Ford had one in the original harness that aftermarket harnesses do not supply.
They expect you to add it. Depending on what style of alternator you have.

Do that first. Even if it doesn’t fix the problem altogether, it is an issue in the long-term to not have one.
 
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428kidd

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Dirt where do you recommend installing the drone to the case? Thanks Lance
 

DirtDonk

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Any bolt that’s convenient actually. But there is a specific stud and nut on the back of the case of the alternator that is usually clearly marked with a “GRD” for ground.

But even Ford rarely use that one specifically at least on Broncos.
The little metal tab that they had sticking out of the main connector bundle was usually next to one of the other studs. So it was connected to whichever one was most convenient.
On my large case alternators I’ve used one of the actual case bolts holding the two halves together as my ground. Simply loosened one, stuck the connector on it tightened it back down and was good to go.
Since it’s directly connected to the case it acts as a ground no matter what.

So one end to the GRD stud and the other end up at the voltage regulator bolt.
 
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428kidd

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Mar 7, 2022
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So I made a ground going from my alternator to my regulator. I also put a new ground from the bellhousing bolt to the firewall. Cleaned the mounting surface where the regulator bolts up at. Drove it night before last late and it's better. It's not perfect and it still flickers some, but it's not as bad as it was. Any more ideas or just live with it how it is? Thanks Lance
 

DirtDonk

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Definitely should not have to live with it.
I know the auto parts stores can test alternators for output, but I wonder if they test them for pulsing?
Some can even test regulators, but I’ve never had that done.
And regulators are fairly inexpensive, even though they’re not very good quality, so it might be worth it just to toss a new one on there again, like you suggested originally.

But there is a test you can do. It’s called “Full Fielding“ and is typically done to test an alternator’s total output. But it also literally bypasses the regulator and might just be able to narrow down the issue.
I wonder if we can even modify the test somewhat. I’ll talk about that in a minute.

Full fielding as where are you jumper the F position to the A or S positions on the regulator connector. This essentially puts 12 V to the field circuit and the alternator so it puts out its maximum current.
If the pulsing goes away then you should be able to tell that it’s the regulator.
In theory… 🙄

Probably best done at night so you can see if there are still any small pulses.

The modified version of that is something I don’t know if we’ve ever talked about here.
Where you could take a 9 V battery and connect it to the F terminal of the connector so that instead of its maximum output it outputs a lesser amount.
That might be a more accurate test if it works.
Anyone see any reason a little 9 V radio battery wouldn’t do the job?

This is all done with the regulator wiring disconnected from the regulator by the way.
 

DirtDonk

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Then again, by the time you’ve done all that you could have a new regulator.
But ask anybody who’s worked on old cars for any length of time how many “spare” regulators they have in their garage and you might get why I am going on and on about testing instead of just buying a new one.😉
 

brncofinatic

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The centech harness I installed was designed to be used on any year, which means there are two ways to hook up the light, depending upon your year. Read the fine print. It tells you to make sure and cover all ends not being used. I chased a flashers (that was flashing intermittently) for weeks. I didn't read the fine print and was shorting across those wire ends. Not sure if that is your problem, it was mine. Jerry
 
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428kidd

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Mar 7, 2022
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Broncofinatic, your lights pulsed? I made sure to cover all unused wires , I always do that just as good measure. So I bought a new napa , there better brand, regular and out it on there. Didn't affect it much . The lights are pretty constant now at throttle. No more going down the road like it's flashing the lights at the car in front of them. Only issue now at night when it idels around it pulses some. Like I say not bad, but it's there still , but not near as bad. Dirt thanks for all the help , I may dive in to it deeper in a few days . Thanks Lance
 
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428kidd

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Drove it last night for the first time since last winter. It was almost dark so I got to use the lights. They still pulse when on. Parking lights , or head lights doesn't matter which one. New voltage regulator. Ground to the alternator case. Good clean grounds to the engine and body etc. New wiring harness etc etc. Just a little update In case anyone has any other ideas.
 

DirtDonk

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Did you ever remove the alternator from the engine mount and make sure that all the surfaces touching each other were clean?
That would be the bolt hole threads, the end of the cylinder head itself, both ends of the round spacer, and the case of the alternator?

And one off-the-wall thing to check.
If you can access it, reach up behind the fuse panel and make sure that the three main power studs and their nuts are tight.
I’ve only run into this once about 20 years ago, but one of the nuts had worked loose, and one of the main power wires was not as solid a connection as it should’ve been.
Awkward, but probably worth the effort just to be sure.
You definitely don’t want to one of those overheating!
 
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428kidd

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Dirt , I didn't remove the alternator no. I did check everything on the front and have ground on all points. The wiring harness is a brand new Centec harness, I don't think it has those lugs ?
 
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