Can an overcharging alternator cause issues with gauges

Alternator voltage output will vary somewhat with engine rpms - less voltage at lower rpms .. Shifting into gear lowers rpm + alternator output.. HOWEVER when rpms increase so does alternator voltage - so instruments should be inop while driving down highway - IF excessive alternator output is indeed the culprit.. You can disconnect the alternator wiring connector or simply remove the drive belt for testing purposes.. ** Do gauges still malfunction with alternator eliminated ?? **