2001 996 alternator failing?

About 6 months ago I had a problem with my alternator regulator failing. I took it to a reputable shop and they rebuilt the alternator with new bearings and regulator and it has performed well since. Recently, I noticed that I can hear a single clicking noise coming from the instrument cluster area and the alternator charging gauge will drop from 14 amps down to just above 12, then recover after a few seconds back up to 14. I've noticed this happens at idle with the air conditioner on. Just wondering if I'm seeing the beginnings of a repeat regulator failure or something else might be going on. Any thoughts would be appreciated. Thx. Jesse

Sounds like a alternator/regulator problem, but... could be a cable/ground/wiring/connection/battery problem. Did you get any type warranty on the alt rebuild..?

There isn't anything in the instrument cluster that would click as part of the voltmeter. But what could be going on is that a fan comes on and the voltage drops. I don't think you have an alternator failure and you may not have had one initially. I think it's the starter/alternator cable. There is a part of that cable that is unprotected from the elements and corrodes from the inside. It make a high resistance point in the circuit that charges the battery. As more fans come on, they draw more current and as more current flows across the high resistance corroded cable, it drops the voltage that you see on your gauge. No existing battery or alternator test equipment is designed to diagnose this cable, but to those who don't know, it can look like either an alternator or battery problem. If you decide to pull the alternator, don't put it back until you replace the cable. Part number: 996-607-019-01. I got advice from a super well known indy that I needed to replace the battery and the alternator, which I did, but when it didn't solve the voltage drop, I had the cable replaced and voila. I have the cable hanging on the wall of my garage.

Does it click again and then the voltage goes back up to 14? Any heavy electrical load on the car - like a motor starting to start but has a locked rotor - could cause the voltage to drop like this. The clicking could be the relay. So it could be a draw and not necessarily the charging. Finally, these cars don�t always hold 14V all the time. My car shows 14V for a while, but after driving for awhile, the battery is fully charged, and the regulator drops the voltage to 12.5 or so.

I'm sorry but I have to call this as not likely. The voltmeter on the instrument cluster is not connected to anything that would click as part of its operation. It's just a voltmeter connected to the battery. The standard evaluation equipment from Snap-On or similar, cannot diagnose a problem with the alternator/battery because they aren't designed to see the issue with the starter/alternator cable. That's in part because the design of that cable is unique to Porsche.

You are hearing the relays click as the radiator fans shift from low to high. The fans draw mucho power on high speed and that loads the alternator down. You probably also have a Y cable that is on the way out.

My thanks to all the respondents. Very helpful information. As I mentioned, the alternator did have a failed regulator which caused the initial problem and led to the refurb by my local alternator shop. They are a mom and pop shop, well regarded and would not have an issue with standing by their work if I brought the alternator back to them. The down side is that I would have to go through the process of pulling the alternator again. I did not notice the clicking sound when at speed, only when at idle with the air conditioning on. I may try to replicate the problem and see if I get the clicking with the ac off. I also did not hear a clicking when the gauge showed the charging recovering to 14 volts. The idea of a relay clicking on makes sense to me. I really appreciate the part number included by 996-CAB. That really helps. I found it interesting that one of the vendors I checked when pricing the cable, says that the part does not fit my car. Strange. The other vendors said it did fit. In general, these cars are getting old and with that, the cables and ground points are getting corroded. I think it's time go through all the ground points and give them a good cleaning. Same thing with the cables and relays on my windows. The joys of owning old cars. Thanks again for the help gents. Regards--Jesse

The voltage drop on the alternator charging circuit certainly can be tested with the proper hook-up and a DVOM... The problem is that to do the hook-up, the alternator must be removed and a temporary test wire installed then re-assembled for testing, then removed again to disconnect or repair.. Another problem is that some voltage drop is inevitable, all circuits have some voltage drop, and much debate on how much is acceptable due to varying amounts of connections, length of wire, current draw, and varying degrees of degradation..... Due to this uncertainty and the common failure of the "y" cable it has become common practice to "just replace it" if symptoms are there.( there is no "line drawn in the sand" ) But "true Professionals" will do the extra step to test the voltage drop and instinctively know when it is too much for the circuit being tested..

Actually, you can test the voltage drop without removing the alternator. You just need a solid copper insulated #10 or #12 wire and a Voltmeter. You strip about 1/2 of wire and bend it to form a hook, then reach behind the alternator and touch the output with the bare wire. Using a friend with the voltmeter, you attached the other end of the wire to the plus terminal of the voltmeter and the negative side to the + jump point while the engine is running and the fans are on. The drop in voltage should be under 1V. Preferably way less. If not, you have found your issue. Or you can do what I did and have your indy wheel out the Snap-on battery and alternator test gear, tell you to replace the alternator and battery, replace both and still not have the issue solved until you replace the starter/alternator cable. I only found out about the voltage drop test after I dropped some serious change. Almost forgot, you can use the bent wire probe to directly measure the output from the alternator.

There ya go, I like that answer MUCH better.....I use the shortcutted technique myself, it saves a lot of time...

I could be speaking out of turn, but I think many of us have more money than time to figure this sh*t out, so we use the brute for$e method.

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You'll recognize that guy because he will have an oscilloscope(Scope) and not just a scanner to troubleshoot vehicles.

Usually I prefer to diagnose the actual issue and not jump to blindly changing parts...but sometimes it is more efficient time-wise, especially if I've seen the issue many times before in similar vehicles. It just bothers me to be a "parts changer" but my time is often better spent elsewhere these days.

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I had one of those Allen SmartScopes once...that thing was 6ft tall 6 ft wide and 3ft thick, took up half a bay...it retailed for $40k in 1980's money ( bought one surplus for $500)... I had it in my 1200 s/f backyard race shop......With it , a STAR tester ( FoMoCo scanner), a DVOM and a Stewart Warner Lab Scope, if you couldn't fix any electrical problem on the planet, it was your own fault.... Nowadays you'd have to PAY someone to take that big azz Allen SmartScope, but the small Stewart Warner Lab Scope will always be valuable.....