pulsing headlights...alternator going?

nostatic · nostatic's Garage

started the car up last night to head to the concert, turned on the headlights, and the intensity was pulsing...no change in engine speed however. Giving it gas didn't seem to change it...they kept getting brighter, then dimmer, then brighter. No apparent pattern. I shut it down and drove the truck to the show.

Is that the sign of an alternator starting to say bye bye? I've been driving it during the day all this week, and the last time I had the lights on I didn't notice this.

cassisrot · 10-03-2003, 06:20 AM

Just went through similar trauma. It was the VR. Check the threads.

Rot 911 · 10-03-2003, 06:22 AM

I agree, the internal voltage regulator is going out. Same amount of labor to get at as the alternator, but cheaper.

scottb · 07:15 AM

Sounds like the regulator. If you're going to replace the entire alternator, Wayne's book, and the Pelican Tech article, do a good job of explaining how to pull the alternator. Now might be a good time to send your shroud and fan to Al Reed for polishing.

surflvr911sc · surflvr911sc's Garage

Is that the original Alt? You’ve seen threads about how to check at the battery. The VR would be my first guess too but if you still have the original Alt then the VR is not on it, it’s beside(on?) the rear fuse panel.

1982911sc · 10-03-2003, 07:14 AM

Same thing here it was the VR. I replaced about 6-8 weeks ago, very doable DIY job. Wayne does a good job of explaining in his book-I just replaced the VR (about $50 or so). My alternator was still relatively new. What is worse though is that my battery literally exploded sometime during the VR failure. I had to replace my battery (Optima this time), and clean out all of the acid, etc. I just coated the entire battery area in the trunk with two coats of POR 15. It looks amazing, and is better protected then before. So, really check you battery that you did not blow it up!

Also, I purchased a Volt-o-Meter and it never did pick this up so it is very sporadic! So don't trust a meter. Good Luck!

Early_S_Man · 10-03-2003, 07:26 AM

If the original alternator type with external regulator is still present ... easy 5-minute job to replace the regulator.

There may be an issue with the alternator brushes ... but they usually cause an occasional flicker of the warning lamp when going out.

A 10-minute test run with an assistant to monitor system Voltage via the 12-Volt accessory plug would tell you if the surges are complete drop-outs -- back down to 12.8 Volts on battery power alone ... or if it is high-Voltage spikes -- above 15 Volts ...that are causing the dim/bright fluctuations.

nostatic · nostatic's Garage

I'll check to see if I've still got the original separate unit. If it is quick to change, $25 is better than $300.

So is it bad to drive it during the day...ie does the extra current drain from the lights make the situation worse, or am I making my electrical system unhappy even during the day?

1982911sc · 10-03-2003, 08:57 AM

If it is the VR, I think you will have surges constantly. It is not related to the lights. That is just where you see it (Porsches little way of warning you that you are soon screwed). Actually I have heard it is better to have on as much as possible, radio, lights, fans, etc as these will all help absorb the spikes in the VR failures. I drove mine for awhile this way and it did end up blowing up my battery, as far as I can tell that is all the permanent damage it did.

nostatic · nostatic's Garage

well, I was going to take Monday off. Looks like I've got something to fill my time...

Jdub · 10-03-2003, 09:11 AM

To be safe, have your battery bench tested and clean all of your ground wires: engine to chassis, battery to ground, etc.

I do agree it appears to be the VR or the brushes on the commutator. If you decide to have the Alt rebuilt, be sure to ask how many more rebuilds they can get out of the commutator following the turndown they will perform on the surface (to get it "flat" to mate nicely with the brushes).

Best of luck,
John

scottb · 10-03-2003, 11:53 AM

I wouldn't drive it until you have the VR swapped-out. No sense risking damaging the electrical system, or cooking the battery.

Embs · Embs's Garage

Quote:

Originally posted by nostatic
I'll check to see if I've still got the original separate unit. If it is quick to change, $25 is better than $300.

Excellent alternator source: $125.94 +core
http://autoexpress.safeshopper.com/684/cat684.htm?276

I have used them many times and they have been flawless.

scottb · 10-03-2003, 11:59 AM

But of course, always check with our host first!

Embs · Embs's Garage

Quote:

Originally posted by scottb
But of course, always check with our host first!

Of course.
All Pelican alternators are new. Even Wayne can appreciate a good deal!

bigchillcar · bigchillcar's Garage

My radio often cuts out, of and on, at night when I'm running headlights and at a stop. In order to avoid this, I have to use my hand throttle and increase idle to at least 1200 rpm's to keep it playing, normal idle is ~950 rpm's. Anyone have solution for this? Don't say don't listen to the radio...

Ryan

Loual · Loual's Garage

While in there repairing, check wires into and out of the fuse box... One of my low beams went out and it turned out to be corrosion of that low beam's wire in the fuse box - simply unscrewed the wire, cut off the corroded part, cut off insulation to expose fresh copper, put it back together, and I could see again!

Early_S_Man · 10-04-2003, 06:21 AM

Ryan,

About your radio problem ... sounds like a classic case of the 'zero-Ampere speed' of the alternator increasing with age! You may want to pull your combination oil temp/pressure gauge, and clean the connectors and Faston tabs for the warning lamp ... and the bulb base, too. Corrosion can raise the resistance in the circuit for the field pre-energizing current, and reduce the current available.

I suggest mounting a 5 Watt, 49 -68 Ohm resistor in parallel with the alternator warning lamp bulb ... per the factory bulletin on upgrading to the alternator with built-in regulator ... posted below.

More information regarding the 'zero-Ampere speed' is located in the following thread:

Alternator question

Jim Richards · 10-04-2003, 06:32 AM

nostatic, I'd also recommend that you don't drive it (much) until it's fixed. I had a VR go south on an old 280Z and it blew the battery. And like a dumb *****, I compounded the problem by opening up the hood to see what made that dreaded sound. Battery acid spray damaged the paint on the fender and my clothes. The VR and wiring were a melted goo. I was stupid but, like any monkey, I can be trained.

nostatic · nostatic's Garage

Quote:

Originally posted by Jim Richards
I was stupid but, like any monkey, I can be trained.

Well, we really should ask your wife about that one...

I'll resist the urge to drive it. Hopefully PP will call me early Monday and say my VR is in. btw I'm assuming I ordered the right one in the catalog - Voltage Regulator, external (for Marchal 55W Alternator), 911/911 Turbo (1975-81)