Voltage reg, Alt, batt, or bad wiring??

My 87 is giving me some weird symptoms lately that I could use help with. I notice that the headlights, fans, etc go from dim to bright and vice versa occasionally. Suspecting faulty charging, I checked voltage in various states at the battery
1) car off, no load 12.9 v
2) car idling, no load 12.3 volts
3) car at 2500-3000 rpm 13.5, then intermittantly 14.5 volts.
The transition from 13.5 to 14.5 volts occurs abruptly rather than gradually.

Confusion has set in because the book says that you should have between 13.5 and 14.5 volts at 2500.

Also, never had a dead/weak battery.

So my question.... bat voltage reg, alternator, battery, or loose/bad wiring.


Thanks,

Scott

It doesn't sound like anything is wrong with the alternator, at least not the 'generating' portion, as I believe it has the 'internal' regulator. The regulator 'module' may be bad, but I suspect wornout brushes, and have seen your same symptoms in a case of worn brushes, twice!

It is a bit of a pain to remove your alternator, but I think the problem is there, and therefore it needs to be taken out for testing/repair. If you can find a shop specializing in motors and alternators, take it there for testing and rebuild. I wouldn't recommend replacement with another unit, because that WILL be expensive, and rebuilding can usually be done for $100 or mabe a little less.

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Warren Hall
1973 911S Targa

Scott,

I just went through a similar problem. My 83 SC was overcharging worse than your car is but I believe that the solution is the same.

I ordered a voltage regulator from **********.com for $55.00 The part is the same for both of our cars. Here is the key: The brushes and are part of the regulator. Thus, you will be fixing both possible causes at once.

Jess

Thanks for the input, This board is invaluable as usual. I think I'll be ordering a regulator on Monday.

I agree this board is great.

I thought "brushes" were things IN the alternator, like electric motor brushes. And I thought the voltage regulator, even on "internal" ones, are really bolted to the back of the alternator.

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'83 SC

Scott,

Take a good digital voltage meter and wire it
up to the car. Drive with it for a while, so
that the alt is warm. My 85 model had a diode
that was going bad and when the alt got warm
it would cycle from 13.9 to 15+ volts... and
even saw 15.5 one time.

Try this and see if it is the same thing. When the diodes do not go totally bad they
sometimes act like this.

The best way to check for a faulty voltage regulator is to check the amperage readings. If the voltage regulator is overcharging or acting faulty, you will see it in the fluctuation of the amps.

Regards


Steve

Pay very close attention to this, when the regulator goes it boils the battery and the fumes and overflow from the battery go all over the interior of the forward compartment. Battery acid is insidious in it's craft.It may leak down into the drain holes and into the frame members and corrode them from the inside.Until I found out exactly what the problem was (reg.) on my 911 I soaked a shop rag in dissolved bi----of soda and draped it over the battery. This neutralizes fumes and hopefully any discharge.


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Wild Willie 88-911