100 amp service entrance wire size upgrade#

so now I decided I will upgrade everything to 125Amps using a New Service Entrance Cable Size of 2AWG (Cu) or 1/0 (Al), the one that comes with 2 Conductors, 1 Neutral and 1 Ground. My biggest concern was about the abscence of a main ground wire from the Service Entrance. Nevertheless, I don't know why there is a Yellow wire connected to the Neutrals, but I think maybe they just ran out of white and use yellow for that circuit. It's crazy how they did it and that's why I will then upgrade it all, especially because I'm afraid that the house Service Entrance from, to and beyond the meter is always hot not matter what, except if the meter fuses are removed. Of course this Main Lug have not Main Breaker and therefore is a subpanel however the problem with this kind of very old setups is that they used the subpanel like if was the main breaker panel but without the main breaker, yeah that's crazy, and even crazier is that I think there is not any Main Disconnect at any point except for the Meter Fuses. That's why I was unable to determine the cables Amp rating by the printings on them. I have noticed the printing in the cables before and read them, unfortunately the part that was left out to the sight have not printing about the Amp rating, just that can be used for up to 600Volts, but all wires including 14/2 and 12/2 wih less amp ratings read the same about 600Volts. Hi PJMax and Casual Joe, What you both stated makes sense to me.