Opel Vectra Alternator.

I have an Opel Vectra 2.0i GL of 1993. I have already changed up to 4 alternators and none of them loads me correctly. When I connect the air conditioning or the fan or simply the brake, the voltage is lowered up to 10.5 or 11V and in normal march they fail to exceed 12.5V What can be the problem?

That depends on your battery amperage.
When a vehicle has A/C the battery must be of greater amperage to supply all the demands of the vehicle.
If you have an alternator whose load amperage is less of the battery, it will never load you.
Check how much the battery and quanto is the alternator.

The alternators are new, because it seems more a carbon or regulatory box problem if it is external that alternator problems now if the problem is always the problem is the alternator and not the consumption of the vehicle. You might have a land problem in the vehicle.

All the alternators that I have put are the originals for the vehicle, of 100 amps. The battery I have is also larger than recommended, it is 72 amps/hour and the one that comes standard in the car is about 55 A/H. Someone has told me that it can be some positive cable that is poorly isolated and some dough current is derived, which would act as an element of consumption. If so I see very difficult to find this cable.

I think you are well aimed with the land problem, it is difficult to find the point where it makes us mass. Any suggestion to discover it?