cbslmb

My headlights, dashlights, and interior lights dim and when the heat or AC is on the blower speed fluctuates. I've already had the battery and alternator tested twice and they tested fine. Somehow the voltage is not being regulated properly. It also seems to dim/fluctuate worse when I accelorate but brightens back up when I let off the gas. Help...?!

ranran

Oh my!

That's almost *EXACTLY* the problem I'm having with my '99 Mercury Sable.

When at idle, I don't see much happening, but as soon as I press the accelerator, Everything electrical starts pulsating and the pulsating frequency increases as I increase the rpm's.

The battery has been tested fine, and the alternator seems to be charging as I've measured ~2volt overvolt on the battery (12v sitting, ~14v running).

I've just recently had the alternator replaced..twice as the first one was bad. The battery has not been replaced, as I never seem to have a problem starting the car.

So, *WHAT"S* going on?

Ran

cbslmb

I know it is wierd. The only thing I can figure is that there is a short somewhere in the wiring harness. Does anyone else have some light they could shed on this matter?

Whymelaugh13

a short doesnt make much sense, cuz whats that have to do with the accelerator?

LDO

I had this problem with my '96 Tarus. When I would accelerate, the lights would dim.

On some cars the computer will kill the field coil on hard acceleration to free up a little bit more power to drive the wheels. The alternator pulls about 1 horsepower from the crankshaft. This is what I thought was going on with my Taurus.

I was wrong though. The problem slowly got worse and then rapidly got much worse. I took the alternator apart and fount that the brushes were completely worn out to the point where the brush wires were running on the slip rings. This ruins the slip rings. However, I had already bought a rebuild kit that included brushes. I cleaned up the slip rings as best I could, put the new brushes in it ran ok.

Within a few months though, the bad slip rings ate the brushes and the problem returned.

As the brushes wear down, the spring force pushing them against the slip rings is reduced because the springs extend. At high engine speed the brushes will float off of the slip rings, momentarily breaking the field circuit, making the lights dim.

A rebuilt alternator fixed the problem

-Lyle

pctoyou

Wow, I am at work checking posts worried that I may not make it home after my 1997 Taurus started showing these exact signs of Light dimming issues upon acceleration. I am glad to see that a Rebuilt alternator will fix this! I had to slow down to under 55mph on way to work. anything over 55 and all the vehicle lights would kind of cycle and dim repeatedly over and over and over! I have noticed a slight dimming efect though for the last 4 months, but My other Taurus does the same thing so I thought it was just normal! Thanks for the information.

Chrisl2003

To EVERYONE who owns a Ford product: Ford's are notorious for their poor electrical systems and components. I drive a '99 Sable and it had the same problem at 21,475 miles, my dealer replaced the alternator 3 times in the first year I owned the vehicle! The car now has 83,000 miles on it and the problem is back again! Also the windshield wipers come on all by themselves and their is no way to shut them off! A new turn signal/windshield wiper switch has been put in but the problem persists. I have replaced a fusible link, both battery cables and the power lead to my starter, the blower motor to the heater has also been replaced (at 43,000 miles). Trust me when I say this, Ford electrical systems are the absolute worst in the car making industry! Volkswagen is a close second!

Davie128

Hi...lots of comments on another auto electric problem. Check my response posted to "Spooky Elecrical Problems" on first page. Don't forget improper grounding will cause a ton of problems, especially on and off stuff. Look in areas susceptible to corrosion. The 'Power Distribution Box' is right up front, getting road mist (real salty stuff where I live in Saint John, NB, Canada). Remove ALL grounds, look for HIDDEN corrosion, clean well, lube with electrically conductive lubricant gel...not light spray and make sure connection is SNUG on reassembly.

Thanks,
Davie128

GuiTarZan

Hi: About this pulsing; If the regulator is in the alternator, the supply/sense wire to it may need to be reterminated. There is too much resistance someplace. The input to the alternator draws quite heavy at slow speed. The output might just keep up with the drain, and the lights would be steady. As the engine runs faster, the alternator load is reduced, the input current drops, and the sense voltage goes up. This might be causing the pulsing also.
Harry