Higher then slightly lower

[230ceBruno]

Since I installed the replacement alternator I find that the cars lights seem to go Higher then slightly normal intermittently. Can anyone tell me why are there potential problems?

 

[wireman]

This sounds like a faulty alternator regulator or brushes, it should of course not occur.
Measure the battery voltage using a dvm if you must but a pointer type indicator will follow the small changes more readily. The battery voltage should be close to 14.2v under normal running (>1500 RPM), if it exceeds 15v lamps will fail and damage could be done to electronic modules.
If the voltage is only low at tick over engine speeds and rises to 14v ish at higher speeds there is no need to worry its just that the alternator needs a little more speed to generate some electrical power.
You may have a poor earth on part of the charging circuit, but the only place where this would have any effect is the engine ground strap which would make starting a bit slugish.
Check the wiring to the alternator, make sure that the small wire has a good conection, it is the voltage feedback (via the warning lamp) from the battery to the alternator and could make for poor voltage regulation if it has a dicky contact.
Was the replacement alternator rebuilt or just a second hand one? If the later have a look at the brushes they may be worn down. There is a spring contact inside the alternator which engages on the brush/regulator assy, make sure it is clean. If you doubt the brush/regulator assy it only costs about a tener for a new one.

 

[230ceBruno]

It was just 2nds