Volt meter in instrument cluster goes from a bit over half (2/3) to dam near 18.. This happens 90% of the time... Other 10%... I just don't notice..

This has been happening since I got truck 2 years ago..
Changes ALL exterior lights to led.. Got proper led flasher. Turn on signal ... And it will rise fall lots.. Lil bit less with all led...

DOES NOT CAUSE ANY HARM TO ANYTHIG...

But I also don't want it to become a issue

Alternator changed year ago

Is there a voltage regulator.

 

Take some readings at your battery with your multi meter while the alternator is under load

See how they look .

Most often the gauge will drop rather then spike as voltage is drawn from the dash cluster Buss bar

Depending just what year your working on they all have voltage regulators some internal to the alternator the older style external most often mounted on the left innerfender.

 

Sorry... Lack of info...
1991 Toyota 4x4 pickup 3.0l

 

Your voltage regulator is in your alternator .

Like I said get some voltage reading at the battery