Help. You can see from video how dashboard mileage light is pulsing. As well i have device showing current voltage it jumping from 13v to 15v all the time. Changed new alternator the same problem. Any ideas someone? maybe there is some voltage regulator witch i don't know?

You Tube

You Tube

Generator Suppression Module------Right Front, Engine Compartment

There is no additional external voltage regulator, only the one inside the alternator. I had similar voltage fluctuation in two cases:
1. When I put in a lithium battery
2. When I tried using a supercapacitor in parallel with a normal led acid battery
The voltage fluctuation completely stopped when I reverted to using just a normal led acid battery.

Or just broken alternator.
Happened to me couple of times in my winter beaters.

Other possible causes could be poor connections of the battery cables so I would make sure that all connections to the master fuses, as well as the connection of the ground strap to the body, are clean and sufficiently tight. Resistance developed inside the crimps of the main battery cables is also a known issue. The crimps may look very good on the outside but there may be some corrosion inside. Check if any of the battery cables is, after running the engine for say 5-10 min., is getting warm/hot.