Q: Is my charging system working properly?

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I have a problem with my Audi A6 2005. It stuggles to start when its cold outside (below 0 celcius). I have replaced all 4 glowplugs, checked the glowplug relays and so on. Still problem. It seemed that the alternator didnt charge properly. So I hooked up a voltmeter on the battery when the car was running. Around 12.8V. Same as when the car is not running. I then hooked the meter directly between the alternator case and the output, the big wire from alternator. About 14,5V. So I guess the alternator is ok. I then hokked it up between negativ on battery and output on alternator - 14,5V Good. Then between positive on battery to alternator case - 12,8V. This will suggest a leaking positive wiring? I think the voltage regulator is mounted on the alternator so the wire from the alternator should lead "regulated-current" yes? Should I spend time on following the wire from alternator to battery, or am I missing something here?

Thanks Ekdal

My car has 155000 miles.
My car has a manual transmission.

The B Positive terminal on the Alternator (the big one) should be linked to the battery via a cable that connects at the starter, so you shouldn’t read a voltage difference between the Alternator and the battery positive terminal. You may have a fuse-link in the cable that is broken or the cable itself may be damaged or corroded. The voltage at the battery when the car is running should be around 14 volts. You’re going to have to get under the car to inspect this. If you would like to have a professional sort this out for you, you can contact Your Mechanic to have a technician come to your home or office to check out your charging system and tell you what needs to be done.

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