Actually the meter in the car is an ammeter, not a voltmeter. It is a simple direct reading of the current passing into the battery. You didn't say what car you have, but 51K's have generators rated at only 35 amps and it increased to 40 for 52-3. Your generator or regulator would, it seems, have burned out by now if that were a real reading. I suspect there is something wrong with your gauge. Check the voltage from the regulator, as advised above. If this is OK, then your gauge is defective. If it is also way high, then your regulator is defective, and needs to be fixed before you burn out your generator armature.