Alternator light - help !!!

Crazy Horse · 01:55 PM

My 1979 3.0 SC was running fine - getting ready to make a cross-country trip.

Rained hard yesterday and had to take her home through serious downpour.

In the past, my red alternator light would, from time to time, come on at initial starting of the day - a light revving and she'd be out for the rest of the day.

Today, on the way home, the light came on and stayed on. I let the whole thing cool down, checked the belt, banged on the external regulator (I hope that black box was the regulator) and light still stays on.

I checked the voltage at the battery while running and it's showing 13.0 volts.

I looked through the myriad of posts on the subject, but none seemed really clear what I should check for next or what the main culprit / solution might be.

Any advice would be greatly appreciated.

WERK I · WERK I's Garage

Is that 13 volts on a fully charged battery? Check to see if the voltage changes with the headlights, blower fan on. If it does not change, then it's either the regulator or the alternator giving you problems.

ischmitz · ischmitz's Garage

Well, measure the battery voltage BEFORE you start the engine - that'll give you a baseline. Then have someone start the engine (don't rev it yet) while you watch the voltage on the meter. During cranking it should go down a volt or two. Once the engine cathes and idles it recovers slightly. Turn the headlights on, too.

Now you should see anywhere between 12 to 13 volts on the meter depending on your battery charge level and accuracy of the meter used. Once you rev the engine and if the charging system works properly the voltage should go up to above 14 volts. If that does not happen you run essentially off the battery.

If that is the case your regulator or your alternator have an issue. It could be a bad ground, bad internal diodes, etc. The fact that your charge light comes on means that the rotor coils draw a field current through the regular and the charge light from the battery. But for some reason the alternator does not generate any power.

Hope that helps,
Ingo

Crazy Horse · 07:36 PM

I pulled my voltage regulator. One of the male pins was broken off and inside the female terminal and looks like it had been in the process of breaking off for quite a while...the film of corrosion/oxidization finally broke the current completely.

Thanks for all the help !!!!!!!!!!

WERK I · WERK I's Garage

Great find! Sure is better news than pulling the alternator.

Crazy Horse · 04:04 AM

Bought a new alternator and voltage regulator. Installed the Voltage Regulator and it works great - dash light is working fine!!!

Close the book on this one. She's running great.

Ready for a long "Road Trip".

WERK I · WERK I's Garage

Excellent!!! Congrats.

911teo · 02-20-2008, 05:38 AM

I am having the exact same issue on a 993... where is the voltage regulator?

jeffrey2 · jeffrey2's Garage

Been following this thread ande a few additional; as i'm in a quandry with my 911.

Voltage with no load (engine or anything else) is around 12.5v; when I start it and run at 2500; it raises to 13.6v. Turning on the AC, Lites, and radio at idle puts the car at 13.2v.

I think it's my battery...when i revved and held at 2500; i let up gas, then cut the engine; the volts went down appx. .1v per second until it got to 12.5v.

My light is on until I hit hi revs; on the freeway it has been known to flicker. Not the ground, checked that.

I am guesstimating it's the battery; any input would be greatly appreciated as I spent upside of $500 for an alternator two years ago and don't want to part with it again unless it's necessary.

Any help would be greatly appreciated.

Jeff