[ertech]

Hi guys .
my car a a 89 Had my tach go wild once in a while but never has anything to measure voltage when that happens.Had my voltmeter in the car and this time was able to measure the voltage . it was at 11.4 and no mater how much I reved the voltage would not go past 11.7. it I turn off the car and let it cool .when I start again get 13 while running at any RPM.
1-why would My alternator light not come on when this happens?
2-I can change the voltage regulator easily but what if it a diode problem what do I do?and is there a way to check this?

Thanks