I recently did an absurd amount in one go: clutch, new turbo, new cat, new starter, new alternator, new battery. Everything seems fine except the electrical system, which is now acting kind of weird.
Prelude: On finishing all the work the car would crank slowly but not start. Being a moron, I immediately assumed it was the starter. Tried to jump the car briefly, thinking they might have sold me an uncharged battery, but it would still not start. Bought a new starter, installed, still no start. Reexamined my assumptions, and let the battery charge from another car for half an hour or so, and it fired right up. So. Thanks Sears! Charge your batteries next time.
Car runs fine for a week or so until today when all sorts of electrical wackiness begins. The instrument cluster backlights began to flicker at a steady rhythm, seemingly independent of RPM. The instrument cluster LCD then flickered and died entirely. When I turned the car off, the voltmeter read ten volts. Ruh oh. Tried to start, and it fired right up, which it should not do at ten volts. Took out the multimeter, I get 12.5 volts across the battery terminals, 14 or so when the car is running, so both alternator and battery seem fine.
Instrument cluster LCD then started working with the ignition on but the engine off. As soon as I start the engine, the LCD goes dead. Voltmeter reads 14 when the engine is running, 8-10 when the engine is off. The fuel gauge starting jumping around erratically. Then one of the headlights went out, only about six months old.
I'm at a loss here. Is it just my instrument cluster going out? What about the headlight then?
All terminals are clean and tight, no alternator/battery service light, everything seems good.
That coil ground seems indeed to be the source of the instrument cluster issues. The bolt was rusty and wasn't getting continuity, fixed that. I assumed the ICM was the only thing getting a ground there; what else uses that ground? A lot apparently.
Still an issue with the battery after fixing the above. It is draining to a no-load voltage of 10.5 volts, sometimes. With the alternator on I get 14 volts between battery terminals. I drove the car for a while and stopped and got 12.5 across the battery, great. Drove some more and got 12.5 again. When I got home though, the interior volt gauge read 12 immediately after turning off the car. To test I turned on the headlights...it dropped to 10.5 again, and stayed there even with the lights off. The starter cranked after that but was slow.
So. Known good alternator, intermittent battery charging. Any ideas?
Update: Battery has a bad cell. Mechanic friend at the Audi dealership took it to work for the day and looked everything over. Alternator, starter, electrical all seem fine. Battery won't hold more than 10.5 volts.
Battery is a DieHard Gold GS48 from Sears. A word of warning: I thought DieHard was a solid brand backed by a solid company. Apparently their quality control has gone down lately and you can find many DieHards coming off the shelf bad.
Sears' customer service has also taken a nosedive. I took the battery back to get it exchanged (it is two weeks old, less than two hundred miles on it). They are giving me all kinds of ****, have "tested" it twice and admitted that it holds a weak charge but they refuse to replace it without me bringing the car in to have my entire electrical system looked at, by them, at my own expense. Nevermind the Audi mechanic's signoff.
I am going back tomorrow to raise more hell, but I would recommend caution when dealing with this once-great brand in the future.