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Discussion summary
YOUR RESEARCHBad Volt Gauge - Now What?
Leading reported evidence
Replace of those items as they can be wear items
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Performed · outcome unconfirmed · Original poster
Probably good I replaced all of those items as they can be wear items, but wow it feels like I wasted a lot of time.
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Suggestion
I don't think you need to check the jump point in the back because if it isn't as high back there, there is no way it is higher at the battery than the jump point because you only get to 14+V when the alternator is working properly.
Leading evidence: 'Replace of those items as they can be wear items' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check jump point in the back' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
I pulled the alternator again, replaced the voltage regulator.
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Performed · outcome unconfirmed · Original poster
The Alternator itself is a Bosch model, (Made in Great Britain), and the voltage regulator was just replaced with a Bosch model (Made in China).
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Performed · outcome unconfirmed · Original poster
Similarly, I had the alternator bench tested (It was good!).
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I was super happy to hear that mine bench tested just fine, as it's an original Bosch unit.
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Check jump point in the back
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Suggestion
I don't think you need to check the jump point in the back because if it isn't as high back there, there is no way it is higher at the battery than the jump point because you only get to 14+V when the alternator is working properly.
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Suggestion
I looked in my books and I don't know where the voltmeter in the dash is picking up the voltage, but I would try and find the connection before I replaced the voltmeter.
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So - I've been chasing my tail a bit lately. This all started with a slow start once the car was warm. I then noticed my volt gauge in the car was reading super low (Barely above 10). I went into replacing the starter and Y-cable. Similarly, I had the alternator bench tested (It was good!). Put everything back together and had a nice fast start. Still had a low volt reading however. I pulled the alternator again, replaced the voltage regulator. Similarly, I decided to replace the battery (It had 2021 date on it - so not terribly old, but maybe on its way out). I put everything back together and decided this time to use a voltage meter and measure (I know, I know - I should have started with this). Probably good I replaced all of those items as they can be wear items, but wow it feels like I wasted a lot of time. I did learn a lot on the way, however....
As you can see in the photos - I'm getting great voltage while idling. But - my gauge still reads low. So - Does this mean my gauge is faulty? How do I go about replacing that volt gauge? I Is there an easy way to pull the gauges without pulling the entire dashboard?
Car is a 1999 (3/98) Manual C2 with ~130k miles on it and otherwise very healthy.
That's very odd. I don't think you need to check the jump point in the back because if it isn't as high back there, there is no way it is higher at the battery than the jump point because you only get to 14+V when the alternator is working properly.
I'm assuming the engine is running these pictures. If so, you have a great alternator and Y cable.
Turn off the engine. Measure the voltage at the battery. It should be around 12.5V. Now turn the key to the on position but do not start it. If the voltmeter in the instrument panel is well below what the battery is reading, then you have something wrong with the voltage gauge in the instrument cluster or its connection. As an electrical engineer, I'm going to guess there is a bad/corroded connection to the voltmeter because the voltmeter in the dash is a super simple thing that either works or shows nothing.
I looked in my books and I don't know where the voltmeter in the dash is picking up the voltage, but I would try and find the connection before I replaced the voltmeter.
Yes - those photos are while it's running. I'll try all of this tonight. Good to hear my Y-cable and alternator are good! The Alternator itself is a Bosch model, (Made in Great Britain), and the voltage regulator was just replaced with a Bosch model (Made in China). The Y-cable is brand new. Yes - it's all very confusing and was initially pretty concerning, but now it's just tracking down where the connection is bad to that gauge in the car...to be continued...
Also, my Indy says the remanufactured Bosch alternators are crap and I found that to be true with mine lasting three years before I could hear the bearing making noise it shouldn't have been making, I just replaced it with a New, not rebuilt Bosch, and it works better.
That's kinda my understanding too. I was super happy to hear that mine bench tested just fine, as it's an original Bosch unit. I actually did buy a replacement unit from WPI that turned out bad straight from the factory (Bad bench test, and overcharged a previous battery I tried causing it to spew battery acid out). Replacing just the voltage regulator on this alternator seems to be keeping it alive.
If your trouble turns out to be the actual voltage gauge, I might be able to provide you a spare, working module from a 2002 C4 Can instrument cluster.
PM me if that turns out to be the issue.
Bahman
The voltmeter gets its signal from the alternator. The same signal is used by the low charge warning light. See the attached pages from the Porsche service manual. I also included the troubleshooting section for the voltmeter. It looks to me like the voltage signal from the alternator should be the same at the alternator output that powers the car. The regulator drives this signal. Check the voltage at what is called terminal 61 in the manual. This appears to be labeled as L on the schematic. If the voltage on terminal 61 is ok then check the voltage on this line at the instrument panel.
Measured at the jump point in the back and am getting 14.3 volts. I think I truly do have a bad connection in the instrument cluster or its connection as you've pointed out. Now to dig in and see about getting to the bottom of it.
Hopefully you are not stressing about this too much. You�ve fixed the big problems, starter and Y-cable and alternator. You�ve proven they are working. The volt meter is a �nice to have� item. Millions of people are oblivious to the voltage in their cars. And having it working won�t make the car faster�.
Definitely not stressing anymore. Initially I was a bit, as I didn't want to run low voltage and potentially damage anything. Thanks to the help of this group I was able to figure it all out. It does bother me having a non-working gauge though, so I'll want to definitely fix that. Not looking for any performance - just want a healthy car and fun driving experience!
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