Charging issue

[bjmullan]

So fitted my rebuild carbs at the weekend and the car fired up first time

But the red charging light didn't go off

Had the battery checked yesterday and it's good to go. I'm away on business now to the weekend when I plan to check all earths etc. Two questions; Any suggestions on things to check? And what are my options for getting the alternator sorted. Do you know of someone that does rebuilds or can you purchase a new one?

Summers coming and I don't want to miss it, I think it's going to be on a Saturday this year!

[mycar]

Does the fanbelt have the correct tension ?

[smallspeed]

I'm assuming your car has an alternator not a dynamo? I think dynamo's are a 356 thing..
Also, assuming the drive belt is actually driving it (ie it doesn't squeak like mad if you blip/rev it)

If you have a multimeter, I'd do the following..

1) Double-check its not charging by checking the voltage across + and - on the battery before and after starting the engine. If it is charging it should be around 14v running and <12.5v when not

2) (this is a general alternator thing, not porsche specific so will require some input from others) make sure there is a 12v signal going to the alternator with the ignition on / prior to starting, to power the coils and start the charging process. On a BMW I think this is a D+ post, not sure on a 911 (or how easy it is to get to). Its usually a small post and the +12v goes to it with ignition on (via the "idiot light"). If the idiot light is on with IGN and doesn't go out with the engine running (plus a few revs to kick it off) then most likely that signal is there but its worth double checking

3) Third thing I'd check (which I'd probably place money on if I was a betting man) is the voltage regulator. I'm not sure if there's a simple check you can do with this because when it went on my old 911 i just removed the whole alternator, fan and all, and took it to a local alternator guy in a tesco bag! He cleaned it all up and replaced the voltage regulator while I walked around the shops down the street for an hour, and charged me about £25..
Others may have a test you can do to confirm the regulator, or maybe its cheap enough to just replace it? I don't know..

Also, it might be more work to get to the posts on the alternator to do test #2 than it actually is to remove the alternator and get the reg replaced (ie test #3) in which case it might be better to do 3 before 2

[scalino65]

3) Third thing I'd check (which I'd probably place money on if I was a betting man) is the voltage regulator. I'm not sure if there's a simple check you can do with this because when it went on my old 911 i just removed the whole alternator, fan and all, and took it to a local alternator guy in a tesco bag! He cleaned it all up and replaced the voltage regulator while I walked around the shops down the street for an hour, and charged me about £25..
Others may have a test you can do to confirm the regulator, or maybe its cheap enough to just replace it? I don't know..

I dont know either, but maybe check the resistance across the regulator? if its sky high then I guess its stuffed.
Also, if the Reg didnt work, wouldnt the voltage in charge at the battery when running be really high or would it simply result in no current flowing to the battery when the car is running?
Dunno, but I'd be very interested to hear more from people who do.

[smallspeed]

In my experience (2 alternator failures - 1x porsche, 1x mercedes, both bosch alternators i think) its resulted in no-charge rather than over charge, but I don't know if that's down to how mine failed vs. how how they can fail

[bjmullan]

Got the battery checked and it was fine. Checked and cleaned connections into the battery and regulator etc. Fired up the engine and no red light

Then went for the first short drive of the year. Oh how I love my 911

[210bhp]

Regards
Mike