Hi All -

I'm fairly sure my alternator (-6) just crapped-out and want to confirm that's the problem. Very abruptly my dash voltmeter dropped to around 10-11V when running, regardless of revs, vs the normal 13.8 or whatnot.

The battery did not seem to be charging, but was just about 5 yrs old so I replaced it, however no change in the voltmeter reading. All wiring and grounds look intact, same as before the issue started. The car starts and runs normally with a charged battery.

Is there an easy way to confirm it is or isn't the alternator with the engine still in the car?

Thanks!

Have you verified the gauge reading with a multimeter on the battery? Is the alternator light on? Belt tensioned?

Referencing a Bentley manual for my 911:
After verifying that your belt is tensioned, electrical connections good, etc
Connect voltmeter to battery
Run engine at ~1500 rpm and check voltage
Voltage much higher than 14.2 = bad regulator
Voltage below 13.5 = bad v-belt, regulator, or alternator….
…Assuming your v-belt is good continue running at 1500 rpm and turn on all electrical accessories. If voltage stays the same most likely cause is the regulator. If voltage drops most likely cause is the alternator.

I think this is a quick and dirty test you can do at home. Alternatively you can go to any FLAPS and they will have a tester that works on similar principles.

You can full field the alternator momentarily - if output on B+ isn’t well above 14v alternator is bad.

http://forums.pelicanparts.com/porsche-911...agram-help.html

See post #12 from spoke
http://www.914world.com/bbs2/index.php?showtopic=64142

The terminals he is referring to are D+ and DF. Per his post - if the schematics and the terminal descriptions doesn’t make sense to you, have FLAPS test it, but as you know, that entails the PITA of removing the alternator 1st to test it.

Thanks guys, very helpful and with so much internet focus these days I kinda forgot I have several old-school service books/manuals in my cabinet

I forgot to mention the belt is fine. The car's firewall is intact/uncut so access to the actual alternator and belt is a beotch. Will do some testing on Saturday.

My 914 doesn't get driven much and I do keep a battery maintainer connected but I bought one of these last year and now have three of them on my vehicles. They connect to an app on your smart phone via Bluetooth and give a charging system health check. $36.

Click to view attachment

Well my son had my/our multimeter with him at college so I borrowed one and poked around a bit over the weekend.

The alternator shaft/bolt does not have an allen hex which apparently is a tip-off that it "probably" has an external regulator, but I'm not certain of that yet. The regulator on the relay board looks (is) old and may not be hot but I haven't figured that out yet.

The battery (new) reads a steady 12.8V or so at the terminals. The dash gauge also seems accurate per the multimeter.

The new discovery is the issue seems to be intermittent as with the engine running around 1500RPM the voltage at the dash popped up to normal-ish briefly, a couple times, then dropped back to 10-11V.

Would that indicate the alternator brushes or the regulator or other? I had been figuring the regulator would just completely fail and not be intermittent but not sure of that either.

Full field it.

If it makes 14v or more then the alternator is fine.

If alternator is good you know you have a bad regulator. If it doesn’t make good voltage you have a bad alternator. It’s that simple.

Duplicate

Got diverted and distracted by a bunch of other nonsense in the last few months, but finally closing the loop on this saga, hopefully!

Turns out the LED for the charging circuit in my custom quad-gauge had failed and shame on me but I hadn't noticed. So NH Speedo opened it up and fixed that. Secondly the ancient external regulator on the relay board had apparently been marginal/intermittent and it totally failed once the gauge was fixed. The two things may well have been interrelated I figure. I also had already put in a new battery previously too, so with luck all should be well.