Would a bad alternator cause headlight flicker?

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Chained_360

Chained_360

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On my 1968 Barracuda, there are a couple issues that lead me to believe my alternator is on its way out... Primarily, there is often a metalling whirring/squealing noise when the engine is running that sounds an awful lot like bad alternator bearings.
Secondly, when my headlights are on, they flicker (in terms of dimness). Are these two separate issues, or do I need to pony up and buy a new alternator or rebuild it? Also, could the headlight issue be a regulator or something else?
 
Flickering headlights usually indicates a regulator aging out, but make sure the connections in the regulator's circuit are clean and tight. Resistance in this circuit can also cause fluctuating voltage. I would check the belt's condition, proper tension, and the pulleys before replacing the alternator's bearings.
 
Alright, I'll run through the circuit with my multimeter and good ol' Mark I eyeball. I just replaced the belt but I'll check the tension.
 
Is this a rapid flickering of the headlights, or do they just dim as the RPM's drop?

Just pull the alternator belt off and start the car and you'll know right away if it is the alternator bearings (or could be the water pump too). Also, hold the tip of a long screwdriver straight against the alternator housing and put the handle up to your ear while running, and you'll hear the bearing whirr coming through the screwdriver if it is the alternator.
 
I've (and others !!!) has written pages on here on this.

1....If you have an old OEM style regulator, that is, electro-mechanical, buy a replacement. So far as I know all replacements are now solid state. Easy to tell, look under. The mechanical has two huge wire wound resistors underneath. The solid state ones do not

This is mechanical:

440-1621-large.jpg


2....Make ABSOLUTELY certain the VR and battery share the same ground voltage / potential. Remove the VR, scrape around the bolt holes, and remount using star lock washers. MEASURE the ground voltage. Do this check with engine warm and running at "low to medium cruise" RPM, first with all accessories off, and again with lights, heater, etc, turned on

Put one voltmeter probe directly into the top of the NEG battery post, with the meter set for low volts. Stab the remaining probe into the VR mounting flange. Be sure to stab through chrome, paint, rust. What you are hoping is a VERY low reading, lower the better, zero is perfect. More than a couple of a tenths of one volt means you need to improve the grounding

3...This can be a feedback caused by poor connections in the main harness. The VR gets power AND SENSE voltage from the blue "ignition run" wire, AND THAT is subject to voltage drop problems on these old cars

The functional path from battery to VR is.....

Battery..........starter relay stud.........fuse link.......through BULKHEAD (red).......to AMMETER......out ammeter (black)........to WELDED SPLICE.......to IGNITION SWITCH CONNECTOR......THROUGH THE SWITCH.......OUT IGNITION SWITCH CONNECTOR.......through the BULKHEAD (ignition run blue)........and to the ignition, VR, etc

Now ANY of the BOLD TYPE areas are subject to poor connections

To check this, Turn the key to run, engine stopped. Stab your voltmeter into the top of the battery POS post. Connect remaining probe to the VR IGN terminal. You are hoping for a low reading, the lower the better. More than .3V (3/10 of one volt) means you need to consider the problem. One way "around" this is to use a relay, l triggerd by the blue "run" wire to feed ignition and VR to relieve the ignition switch.

PLEASE READ the Mad article: Gives a VERY good overview of the what hows and why of problems with these girls

Catalog
 
I am having a similar issue.....I but the weird thing is it all checks out fine with the ohm meter. Almost nil voltage drop through the bulkhead connections.....cleaned them up and die electric greased them. No drop on the field wires. Case is grounded on the regulator.. good reading with ohm meter from battery negative to reg case. Good clean new cable from engine to bbattery and bat to body.

Charge voltage is 14.8 or 9 while revved. Engine warm. I just think tthat's to high. Iam an electrician by trade.....i have went through this whole thing with a meter...only thing i can think of is new voltage reg sucks. Anyone make an adjustable Solid state?
 
If you actually did what you said, you can NOT check these with an ohmeter. You must check voltage drop. The proof of whether or not the VR set point is "on target" is "what is?" the running voltage between the VR IGN terminal and the VR mounting flange?

With the engine warm and running "low to med cruise" RPM, if that voltage is within the set point recommendations (for me that boils down, no pun, to 13.8--14.2 warm) then regardless of what the battery is doing, then the VR is doing it's job.........regulating voltage at it's input terminal to that setpoint

The problem with actually CHECKING this is that EG the 70/ later cars, you cannot easily access the VR ign terminal, without, say, using gater clips or build some adapter, etc, or just clip to the ballast "key side" and use that

So far as automotive resistance checks "in general" the higher the amperage the circuit, the less resistance checks are reliable. Not only must the reading be incredibly accurate, and isn't, but you must be able to connect with the probes "solidly" in such a way that the probes themselves don't affect the reading, and last, some "problem" connections can CHANGE with amperage, leading you down the primrose lane.
 
I used resistance to check across the bulkhead leads....as in engine side and car side. and I did check voltage drop on the main + same way. .1v.
Used ohm meter to make sure I had no broken wires.

Checked again tonight on my vr ssense wire. Its llow like 12v key on. My battery at rest is 12.5. Luckily for now Ihave a relay there for my tach. Better. 14.6 to 14.7. And
no more 15v once in a while. But I'd like a bit lower.
 
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Question. this vr switches the field coil on and off. Does it switch the negative off and on and the other side of the coil is positive?
 
Late model isolated field switch on low side to ground. Early alternators switch positive because other field end is connected to ground at alternator case.

Posting on this thread brings confusion, because a 68 Barracuda came with early alternator. Can we assume eh-body is late model?
 
cdnEHbody said:
I used resistance to check across the bulkhead leads....as in engine side and car side. and I did check voltage drop on the main + same way. .1v.
Used ohm meter to make sure I had no broken wires.

Checked again tonight on my vr ssense wire. Its llow like 12v key on. My battery at rest is 12.5. Luckily for now Ihave a relay there for my tach. Better. 14.6 to 14.7. And
no more 15v once in a while. But I'd like a bit lower.
Click to expand...
If this is 12v key in RUN, and with the engine running at fast idle RPM's, then that is low. You can have voltage drops in the ignition switch and its connection(s) as well as the bulkhead connections. So a complete trace of voltages are in order, from the battery + to the starter relay big lug, through the bulkhead connection, into and out of the ignition switch, back through the bulkhead connection, and on to the VR.

So is the flickering gone?
 
It still flickers. The engine was in park and running. It was 11.9 to 12 which I feel is too low. all of the starter /relay connections have been cleaned and greased and show almost no drop. this car was a low mile granny car. The bulkhead connections looked very good but I did my work and cleaned all the pins anyways. And cleaned the connectors around the steering column. But, probably the ignition switch would be my guess where the drop is. But I'll probe the other bulkheads again later. I will also try a standalone field wire to the alt.

so this field in the alternator is completely isolated? Could be controlled negatively or positively if I change up the field wiring with a regulator of my choice if this one is shitty
 
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cdnEHbody said:
It still flickers. The engine was in park and running. It was 11.9 to 12 which I feel is too low. all of the starter /relay connections have been cleaned and greased and show almost no drop. this car was a low mile granny car. The bulkhead connections looked very good but I did my work and cleaned all the pins anyways. And cleaned the connectors around the steering column. But, probably the ignition switch would be my guess where the drop is. But I'll probe the other bulkheads again later. I will also try a standalone field wire to the alt.

so this field in the alternator is completely isolated? Could be controlled negatively or positively if I change up the field wiring with a regulator of my choice if this one is shitty
Click to expand...

Yes, field is isolated, which is the correct term. Many call these "dual field" which is incorrect. There is no "dual field," but it's slang referring to two field connections.

Yes, you could put any VR you can get in there, but why? These VRs as long as they are a quality replacement have a low failure rate and good track record.

Sounds to me like harness voltage drop is the issue.

IF THE VR cannot see the true battery voltage, then it's not the VR fault. It's the fault of the harness / terminals / connections. If the VR IGN terminal runs at correct voltage when running, then the VR is doing it's job regardless of battery voltage.

Sort of like Mom yelling at the kids. Mom did the right thing. She tried to stop the kids from doing something stupid. That does not mean the kids will stop.
 
But it's seeing a true monitored voltage right from the battery from a relayed 12v now....so next I'll try a new field wire temporarily. Oh, I also cleaned the ammeter connections and checked for tightness. If this regulator turns out to be iffy I have access to a high quality adjustable isolated field I have used on many a bike install that have excited field alts. It quit boiling battery's on my 74 Xs650

oh and new grounds everywhere. Right to the case from the battery with a star washer. No voltage drop at all there.
 
Well you lost me here.

Here's what I do

Divide the system into "parts"

The field VR circuit

The main output circuit

The component parts of the circuit

So start with

1......"what is" the battery doing?

..........when running at low/ medium cruise RPM with accessories off?

..........same thing with loads, headlights, etc turned on?.............

2.....What is VR IGN terminal doing RUNNING as above compared to BATTERY? This is a DIRECT measurement, from battery positive post to VR ign terminal IE ballast terminal

3....The output circuit is almost secondary. If the VR terminal is at 14 or therabouts, then you measure from alternator output stud to the battery pos. post. This drop is the voltage loss from the alternator, through the bulkhead, through the ammeter, back through the bulkhead, to the battery. On say, a hard charging (low battery) and 60A alternator, that can amount to as much as a volt or more on factory wiring. THIS ONE VOLT or more can be considered "normal" "for these cars" with those given conditions......a low battery........a big alternator......means drop Ideally? Of course it "should" be less

4....So if the VR is "same as battery" but it's LOWER than 14V, maybe the alternator CAN NOT keep up. So check the alternator.........."full field"

Read the shop manual. Do a field current test. Use "clip leads" to apply full battery to the field and see if the alternator can output enough power.

I almost seems like you are say the last is the case
 
Oh, and just to be clear. The regulator was monitoring the blue wire, factory wire. I switched it last night to the relayed 12v close by that I use to power my tach. It did drop a bit. But I think it's to high still.

Might have to go get my fluke from work. All I have is an old analog at home.
 
a regulator aging out
Click to expand...
If this regulator is original to the car, after 40+ years, it may be just senile. Try a substitution with a new one. If the problem persists, then you will KNOW if it's circuit or alternator related.
 
I had same problem . All lights flickering after I changed to a 90 amp alt. Changed to solid state reg and problem went away.
 
6 years ago I had this too in my 68 Scout. Did all the checks and cleaning. Finally a new regulator, electronic, kept voltage and lights rock steady. On average these electro-mechanical units can cycle up to 200 cycles per second(Hz), to our eyes that's steady voltage. Points pit or oxide, pivots wear, coils break down, in a harsh environment of heat, cold, humidity, vibrations; it's amazing they last as long as they do before they go senile or quit.
 
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I did check my battery voltage again. 12.5. Alternator stud to bat negative 12.5. Analog meter. Could be a hare less. But so far so good.

I'll try some temp field wiring to nite. Not sure if it's the original reg.
 
Do some checks at fast idle (around 1500 RPM). Things are not spec'd at curb idle for this; all the numbers are for some moderate RPM's.
 
Well. Tested at cold fast idle with new field coil wires. About 14.9 cold fast idle. After warm with a fast idle it's still at about 14.7 -8 volts. Lights flicker. With field coil unhooked no charging action. in drive with slower idle it goes dimmer due to less alternator speed like it should.

I think I will replace the regulator. But with an adjustable one made in the u.s.a. for excited field alts from Oregon motorcycle parts. I'll start a new thread when it arrives.
 
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