I took my car to the shop to get the brakes checked out and noticed that while it was idling (it was dark so I had the lights on) that the head lights and also a light inside would get brighter and then dim and fluctuate up and down in brightness. Is this an indication of an alternator on its way out?

 

Do you have an electric fan or anything else that runs part time? Something that draws juice and then shuts off?

Check the cheapest and then work towards the most expensive. Check the belt for tightness (not too tight) and dry rot, does the belt make your fingers turn black. Check the battery, make sure that it holds a ~12 volt charge when the vehicle is not running. Check while the car is running that the battery is receiving a ~14ish volt charge. Check your wire post on your alternator and make sure that it's not loose. Unplug your battery while car is running to see if the alternator is sufficient enough for the car to keep running without battery. Look at your alternator and see if oil isn't coating the bottom of it, possibly from small leaks in the front main seal. Oil can get inside the alternator and cause it to not recharge that it should.

If it is your alternator, you can take it apart and clean out the brushes and the magnets. That can buy you some more life out of it. Also, tighten up the post on the casing, sometimes that can get loose.

Also, you might want to think about changing your three wire 30a generator for a single wire ~130a alternator, if you're still using the original. You may have put in some aftermarket lighting or radio etc which could be pulling too much juice out of your stock generator.

James

 

nope that's normal assuming it would get brighter as RPM increased. Did that increase in brightness occur when you revved up the engine slightly?

If you didn't see a surge in brightness as rpm increased that would indicate a failing alt.

If its changing brightness and the RPM is idle steady...that might be a bad ground it should also do the same thing at 1500 + rpm...but maybe not

-Gun

 

Dang, one more thing to miss about driving a Mustang. I clearly remember saying goodnight to friends in High School as the car idled, and the headlights alternately dimmed and brightened. I definitely have "I need a Mustang now" itis.

 

I plan on adding an aftermarket A/C system, so I figure I might as well go ahead and change the alternator anyway. The brightness changes out of sync with the rpm and idle, so it sounds like the alternator is going bad. I guess it gives me an excuse to get the 100 amp one that will work better for the aftermarket stuff I plan on installing.

 

I'm not a big fan of one-wire units. I'd recommend a 3G conversion instead. Much more power potential there.

 

Don't mean to hijack but I have a similar question. I have a new alternator, new voltage regulator and headlamp relay. I put in new modern headlamps and they blew within a few minutes of use. I thought maybe they were faulty and put in a new set. They blew too. Put the old ones in and they are fine. I put in a new stereo. Now when I let off the brakes, the stereo shuts off. Some sort of power interuption but the fuse doesn't blow. The lights do pulse a bit. I'm stumped. Any ideas?

 

You need to check the voltage and current flow out of that new alternator and if you wired it up correctly. It's really hard to blow a headlight out even if it is a cheep one. the brake issue may be unrelated so you need to isolate the radio fuse and check what is going on there. As far as i know the radio and brake lites feeds aren't on the same circuits.

 

what can cause headlights to flicker? replaced voltage reg, checked all grounds, replaced dimmer switch, and light switch, alternator put out 14+ volts. I installed a one wire alternator, works fine but no head lights???

 

When customers bring their classic cars into the shop with the any of the above described problems 90% of the time it's the engine block-to-body ground.

Some guys don't even bother putting one back on during their "restoration".




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