Replacing alternator ?s
 

Hello I have a 1987 Porsche 944s it has a new battery but the voltmeter is reading low, I has able to jump it to get it started but it took about 20minutes then it started just fine for 3-4 starts but now it won't start again. Any ideas? If it's the alternator how hard is it to replace any one have step by step instructions? Thank you.
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this could be a number of things, including bad grounds, bad regulator, etc. etc.

i would get it running and take a voltage reading right at the battery terminals with the car turned on. that is where i would start.

in my 30 years of ownership I've gone through 3 regulators. the second one was apiece of crap from FLAPS. The bearings in the alt seem to be almost bullet proof (hope I'm not jinxing myself). so if your battery is good, check your regulator.

I agree with JAX, I've put 2 or 3 regulators in my alternator over the past 24 years. $40 part. Removing the air box and intake duct that runs over top of the alternator lets you get to the back of it without having to remove the unit entirely. There is also a cover that goes over the back for cooling the alternator that has to be removed to access the regulator that simply slips in the back and is held in place by two bolts. Be sure to disconnect the battery before poking around back there.