So I started with the alternator test as the wsm suggests. The readings are all ok except from the resistance which about 0,5Ohm less. This is likely due to the poor state of the connectors. Anyway I continued with regulator test. First test was ok (around 4,9 volts) but during the second I got the same readings that I already mentioned. What I noticed is a poor state and corrosion on the alternator cable connector. Additionally I opened the alternator itself as the test suggests to adjust the metal connector inside. What I saw there is a little bit of dirt-corrosion, I am not sure, while on the first relay ( where I got the normal results) the contacts look like new. Anyway I will change all regulator cable connections and run the test again. I hope it will something simple like that and avoid spending money for a regulator.
I also seen new alternators with the regulator within but this is even more money and new cable lines.
I will update the post soon! Thank you all!