Porsche Repair: electrical, alternator wiring, tight belt

Question
hello dave,i am  owner of 1983 944,just put in my third rebuilt alternator in a year and  after about 2 months after each one still discharging.sometimes when going up hill or under demand the charge gauge will jump up for short time.battery is new,cables tight,belt tight.battery light also comes on.appreciate ant ideas.thanks kevin

Answer
Kevin,

I'm a bit unclear on the exact sequence of events, but I do get the notion that your 944 eats alternators.  It's hard to imagine three or even two randomly purchased alternators with the same exact problems.  It must be something other than the alternator.  I've checked the wiring diagram for your car and the alternator has a built-in regulator.  You do not have a separate voltage regulator do you?

Let's take this one step at a time.  I don't know if you're the first owner or the sixth owner, so let's verify the alternator wiring.  DISCONNECT THE BATTERY.

1.  You'll need a continuity tester, here's what I want you to do.  Remove any wires (mark them for replacement) from the alternator.  Place  one probe of the continuity tester on the alternator case.  Put the other probe on the negative (to ground) terminal of the battery.  The tester should change from a reading of 1.00 to .001.  If it's not at .001, the alternator itself is not grounded well enough.  This likely means the engine is not grounded well enough either.  If this is the case add a ground strap or two to the engine and recheck the alternator for a .001 reading.  If you didn't have .001 before and you do after the installation of ground straps, the alternator you just bought should last you almost forever.

2.  If grounding wasn't the issue take a look at the two wires that you removed from the alternator.  One's red, one's blue, right?

Verify the wire ends are well secured to the wire connectors...and they are spotlessly clean, and are bare metal.

Trace the red wire to the starter.  With your continuity tester, test each end of the red wire for another .001 reading.  The blue wire is the tachometer lead, and shouldn't worry us at this time.

Get back to me using the follow-up question feature of All-experts.  I'd like to hear from you covering the results of your testing.  Til then...

Dave