My 1986 corvette just started showing 15-17 volt on the dash sometimes

My 1986 corvette just started showing 15-17 volts on the dash sometimes, only when it runs for a while it would go from 13.5 to 17 volts and then back to 13.5-13.9 in park with everything on and 12.9 under load or in drive.I checked the battery and the alternator with a multimeter and it read 14 volts all day long. The dash lights do get brighter when it hits the 15-17 and flickers a little. I checked the codes and there was a 53 high voltage that came up but the check engine light has not stayed on. could there be a issue? could this do any damage? also whould cold weather hurt the digital dash? let me know what u think. thanks    

with your digital volt meter... set it to 20 volts scale..   with the engine running and the head lights on..   measure between the battery negative and the engine block...

you should have less than 0.05 volts...

between the negative battery post and a chassis ground... less than 0.02 volts is what you should see...

this test takes about 2 minutes to do.. and will tell you if you have bad ground wires or dirty terminals... this is a voltage drop test..   it can only be done with current running through the wires..

if there is a difference in ground..   you will see a voltage on the meter..  

you might also want to make sure that your battery cables are totally clean..

when the grounds get intermittent .. things can blow up...

measure the voltage at the battery its self.. see if you can monitor any spikes ...

if the terminals get dirty  come loose...  the alternator has no plate for the current to go .. and the voltage builds up...

it is also possible that the alternator or voltage regulator is on its way out..