Triumph Repair: low voltage readout , whats the problem, tr 6, advance auto

Question
I recently purchased a 1975 TR-6 and while driving it my mechanic noticed the readout on the gauge was less than 12...So I purchased an rebuilt alt from Advance auto, with the built in volt.regulator. I installed the alt. and it reads 12.35 volts on my tester. What else could cause this problem and is reading less than 13 volts normal? What else can I check to correct this problem? thank you

Answer
dean, i think 12.35 all though a little low is ok. turn all lights & blower moter on and check it again with your meter. make sure it steps up to handle the load. also it might read 12.35 until you start driving then go up a little. 13.00 to 13.5 is ideal though. if need be go back to advance ( which is where i go) and see if you need to exchange it. dave