pulsating headlights on '92 model

I am having a prob. with pulsating headlights and dash, and an alt./battery light doing the same at idle. The pulsating seems to diminish when the idle goes up. The alternator has been replaced with a new one from the local autoparts house. My Nemisys says the alt. is putting out right over 14 volts steadily. I am in the process of replacing the fan clutch and belt tensioner. Could the weakened tensioner be the cause of the headlight issue? The belt doesn't seem to be loose enough to slip, and there is no squealing from the belt. However, the fact that I can pull on the belt with my hand, makes me think that the belt tensioner is weak. I do believe that the voltage regulator is built in to the alt. on these cars. Having recently replaced the alt. and checking voltage, I am wondering what else could cause these problems. Any help would be appreciated. Thanks in advance.

...I do believe that the voltage regulator is built in to the alt. on these cars. Having recently replaced the alt. and checking voltage, I am wondering what else could cause these problems...

Double check ALL the engine to chassis ground straps, maybe add a new one for good measure.

Tensioner specs are writen somewhere (I can get you 1996). It should run at least 100k miles before the bearing goes bad, I havn't heard it loses tension.

I would still suspect the new alternator / regulator / diode bank, just because I've seen several new ones fail too.

Grounds look good. I will try putting another one when I see the car again. I replaced the tensioner, and sure enough, the belt got alot tighter. Also noticed the bearings on the idler pulley bad, switched with the old tensioner pulley, it worked (LOL!!) Problem still there, though. The alternator has alot of oil residue all over it, maybe a sign of problems with the "new" alternator. I am going to get this one checked out. Thanks for your reply.

I am having a prob. with pulsating headlights and dash, and an alt./battery light doing the same at idle. The pulsating seems to diminish when the idle goes up. The alternator has been replaced with a new one from the local autoparts house. My Nemisys says the alt. is putting out right over 14 volts steadily. I am in the process of replacing the fan clutch and belt tensioner. Could the weakened tensioner be the cause of the headlight issue? The belt doesn't seem to be loose enough to slip, and there is no squealing from the belt. However, the fact that I can pull on the belt with my hand, makes me think that the belt tensioner is weak. I do believe that the voltage regulator is built in to the alt. on these cars. Having recently replaced the alt. and checking voltage, I am wondering what else could cause these problems. Any help would be appreciated. Thanks in advance.

is the engine idling rough? might be something mechanical.

usually when there are a lot of items on (I.E. wipers, air condition/defrost, radio, headlights) once you put your foot on the brake, the lights and everything dim. this is because the alternator is struggling to keep the power going to everything that is operating, including the engine. in my opinion, it sounds like your alternator is on its way out. does the car struggle starting up? has the battery been replaced lately or do you remember the last time it has been replaced. let me know.

I am going to get this one checked out. Thanks for your reply.

Check back when you can, and let us know what's next :)

No, there are no accessories on. The car was also given a tune-up recently. It runs good now. At night, if you start the car without any light or anything, you can notice the green lighting for the odometer pulsating just like the headlights when you turn them on. The battery light barely comes on during this, it is more like a flashing or pulsing. The pulse is the same as everything else that is pulsing. If you give it gas, it goes away until it returns to idle. During this acceleration though, the headlights and everything else continues to pulse.

...headlights and everything else continues to pulse...

That sure sounds like a bad diode..
In the old days I'd say that sounds like a bad regulator..

You did say you changed the Alternator and both new and old ones had the same problem?

That sure sounds like a bad diode..
In the old days I'd say that sounds like a bad regulator..


i agree

Go to a parts store and purchase an amp meter KD makes one which you hold over the battery cable and check amps. You either have a drain or a bad alternator.
Use a 12v test light disconnect the neg. battery cable. Clamp the light on the cable if the light stays the battery has a draw. You may have to wait until all door lights are off.
I would find an alternator rebuilder with a good reputation and pay to get your alternator checked most will do this free but expect you to let them fix it if it is defective. You have to remove and take it to them and get it bench tested.
I used to own a shop and alternators were a big problem area until I found a good rebuilder.
Like the other poster stated they will work with a bad diode and put out voltage but not put out enough amps.

Thanks for the reply. I have already checked for a draw, none present. I am really leaning towards the alternator on this one. Soon as the car comes back, alt. is coming off and going to get checked.

Did you check the voltage with the engine idling. A C on headlights on fan in high and the wipers on.
This should give you a quick idea.

yah, the voltage stayed right above 14 volts the entire time.

A bad rebuild can cause a small alternating current which causes problems. Did you have this problem before replacing the alternator. I think you have to set the voltmeter to A.C. check if you get a reading. Also check from the alternator case to ground and check the hot side. Also disconnect the neg. cable place the ohm meter on one end and to the car frame by the headlights to determine if you have a good ground. Hold the leads together you shound get close to this reading from the cable to the bolt. You should have a ground connection close to the headlights. Use sand paper and clean the connections if poor ohm readings. Uplug the plugs for the lights and use contact cleaner or brake clean. Check the ground from the engine to the firewall.
Clean both battery terminals.
An alternator makes 115V A C and this is converted to D C
I called the man at the alternator shop I use and he immediately said the regulator is pulseing. I never had this problem but I'm sure he has encountered it in the past.

I realize this post is quite old, but I'm hoping (long shot) if there was a resolution to this. I have a 90 Lincoln TC with the same/exact problem. Any help? Thanks.

[QUOTE=90TC;5924664]I realize this post is quite old, but I'm hoping (long shot) if there was a resolution to this. I have a 90 Lincoln TC with the same/exact problem. Any help? Thanks.[/QUOTE


unfortunately, customer got rid of the car before anything else was done to it... sorry.

Use a DVOM and check if the voltage is going up and down. Once you determine this it will give you ideas on what to check.