alternator or voltage regulator

[fizeus]

Hi all,
Yesterday i took my 911 2.4T 1973 for a ride.
After about 150km the alternator red light in the deck (in the oil gage) has come up.

It dims when rpms are over 3k.
Reading on i discovered that this can be alternator (i really hope no) or the voltage regulator.

My batteries are from 2008 but they seems still good. Could this be a worn battery problem ?

How can I diagnose if this is a battery, voltage regulator or alternator problem ?

Can anyone tell where the voltage regulator is located ?

Thanks in advance


Add on: in prevoius days i noticed that at idle the alternator light was lightly on, but it was visible only at night. I also noticed that headlight had lower intensity when engine was idling.

[E Sully]

Put a dc voltage meter on the battery. It should read around 12 to 12.5 volts with the engine off, and around 13.8v with the engine at 2,000 rpm. Voltage regulator is rectangular object on the upper front of the engine bay console just before the ribbed CDI box.

[wwest]

Originally Posted by E Sully

Put a dc voltage meter on the battery. It should read around 12 to 12.5 volts with the engine off, and around 13.8v with the engine at 2,000 rpm. Voltage regulator is rectangular object on the upper front of the engine bay console just before the ribbed CDI box.

Loose drive belt?

Otherwise..

Measure the voltage across the battery posts AND in the engine compartment(***1) with ALL electrical loads on and engine ~2200 RPM. More than 0.50 volts difference(***2) and you have to much rear to front voltage drop.

Most commonly engine to chassis ground connection or alternator output connection at the starter solenoid.

***1. Between engine fan shroud and left end of the top most fuse shown.

***2. Typically ~0.25 volts

[fizeus]

Can this behavior be due to a bad spark cable ?

I remember that simply touching the spark cable number 4 I've got a shock. (Obviously I'havent tested the other cables)
I've also checked for little sparks from the cable to the engine head but i'ven't found any.
I know many suggest to spray water near the spark cable. I haven't done this test because I think this can be dangerous for the engine.

I was wondering if the alternator light can came on in case of electrical dispersions from the spark cable to the engine body.

[T77911S]

plug wires have nothing to do with charging. but, sounds like your plug wires might be going bad.

water does not hurt the engine, just dont spray into the intake with it running.
i hose mine down from time to time. usually before i work on it.

pull the alt and take it to a shop and have it tested. could be brushes, diode or bad winding.
take the regulator, they should be able to test it too.
you might just consider having it rebuilt while it is out.