so the tach doubles as the volt meter...knew that already. i changed my alternator today, which has been bad since i got the car (just got legal within last week)...so my question is when i still had the bad alternator, at idle the tach would switch over to volts, then you give it some gas and it switches back to tach...now with the good alternator, all it does is the tach function...is this how it is supposed to be?

 

I belive so mine done the same thing.

 

voltmeter when the key is in the accessory position then when you crank/get it running, changes to the tach.