1975 911 Alternator & EGR light come on

[Tarek307]

Hi, i have a 1975 rite now when i got it the alternator was bad car would have to be jumped and would run for a bit till battery ran out and the G light would stay on all the time even with car off and key out- so i just got new alternator installed and the car starts and charges right, but when idle gets low the G light & now also the EGR light come on..when you step on it they dim then go away for a while, but back again.

The battery which is in the car is only 2 years old and with brand new alternator now i dont think the battery would be issue.

. Car runs fine, charges fine now..but those 2 lights come on G & EGR

The mechanic which installed the new alternator for me said some of these cars do this and not to really worry about it..however i dont think thats the case.

-i searched and seems some people had this issue but of course the posters didn't give a crap to update their threads with the solution.

[timmy2]

Original style remote VR or internal VR on the new alternator?
If updated to internal style there is possibly a need for a resistor to be installed across the lamp.
There is a tech bulletin covering it. There was also someone selling them as a kit in the classifieds a while ago.

[Targalid]

You can answer most of your questions with a voltmeter. I like the plug into the cigarette lighter type because I can sit behind the wheel and rev the motor to get an idea of how the charging system is working. Others prefer a voltmeter that you can use at the battery to give a more accurate reading. My alternator charges at around 14 volts at pretty much any rpm. A fully charged battery should give at least 12.6 volts with the car turned off. This is a place to start. Here is a link for a cheap voltage meter that you can monitor as you drive. https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0/ref=sr_1_5?ie=UTF8&qid=1503588555&sr=8-5&keywords=cigarette+lighter+voltage+meter

[Tarek307]

Thanks guys- keep the replies coming

[timmy2]

More replies may appear with some answers from you.

Internal or external VR (voltage regulator)???

What are the voltage readings at different RPM's and when off??

[timmy2]

Alternator Help Please

If you now have an internal VR.

[jferrante]

Originally Posted by Targalid

You can answer most of your questions with a voltmeter. I like the plug into the cigarette lighter type because I can sit behind the wheel and rev the motor to get an idea of how the charging system is working. Others prefer a voltmeter that you can use at the battery to give a more accurate reading. My alternator charges at around 14 volts at pretty much any rpm. A fully charged battery should give at least 12.6 volts with the car turned off. This is a place to start. Here is a link for a cheap voltage meter that you can monitor as you drive. https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0/ref=sr_1_5?ie=UTF8&qid=1503588555&sr=8-5&keywords=cigarette+lighter+voltage+meter

I have one of those voltmeters as well..on newer cars the alternator kicks in after 30 secs or so...is it the same with these? Also modern cars charge at like 13.5+ volts...what is the charging voltage for the 911? I am seeing ~12 while running

[timmy2]

Should be charging at 2000 rpm at about 13.5 to 14 volts.
My alternator kicks in after starting and seeing about 1200 rpm.

[jferrante]

Originally Posted by timmy2

Should be charging at 2000 rpm at about 13.5 to 14 volts.
My alternator kicks in after starting and seeing about 1200 rpm.

Ok - I just checked as I give it gas it gets upward of 13v but at idle ~800-900 rpms its 12v or less...sign of bad alternator?

[timmy2]

Could just be a discharged battery. What does your voltmeter read at 4000 rpm?

If you see 13.5 volts and battery voltage doesn't improve at idle after taking your car for a good 1 hour run of it charging at 13.5 or so volts, have the battery tested, they can fail early.

Or throw a charger on it overnight to see what it reads in the morning.

[jferrante]

Yea new battery - will take her for a drive tomorrow see if charging it helps the idle voltage

[Tarek307]

Guys never got to bottom of the issue as the engine ended up seizing on the car lol. however i assume maybe its just because a new alternator was added and i hadn't changed the battery yet.