Some time ago one late afternoon we decided to take the car out for a spin. Everything was fine; the sun set and we turned on the lights and it ran fine for some time until the alternator light started flickering. We decided to head back but otherwise the car ran fine. Sometimes the light would go on or off regardless of the engine rpms. Sometimes even the light would come off when the rpms came down (which is the reverse of what logic would tell you). We stored the car and didn't use it for at least another week. Took it out during the day a coupe of days ago and the alternator light didn't come on; we were not using the car's lights this time because it was daytime.
The belt is not loose, there are no weird noises. My last alternator failure was about 9 years ago and it turned out to be the bearings; which were replaced by a specialized shop. At the time I bought a new Brazilian Bosch unit which is the one in the car now, and I stored the other unit, which was repaired and which I still have, as a spare. My VS ever since new always had a very dim alternator light when the lights were on. When I replaced the original unit it still did the same thing. The ground strap from the transaxle to the chassis is solid. I am suspecting a ground issue somewhere; I would like to hear if any of you had a similar experience and maybe a possible fix for this. Thank you all.