Hi.

I have a rather "big" sound system in my 2005 S80. This is why I changed the stock 140A alternator to a 160A alternator from a 2004 XC90, which was the biggest I found.
I later upgraded my stereo to a Pioneer 80PRS and it had a voltage readout on the screen.
I have been following this voltage now for a while and it seems to change, roughly depending on the outside temperature.
In the summer, when it's hot, it usually stays between 13,6V and 14,0V.
Then in spring and fall, when it's 0-10 degrees C, it stays between 14,0V and 14,4V.
And only in the winter, or when it is negative degrees C, I get the rated 14,7V charging.
I have tested with a multimeter, that these are correct.

The problem is, with the sort of batteries I use, I can not use nearly the full potential of them, at anything below 14.4V.
I am planning on diode modding the alt to charge at 15,2V-15,5V, but I would have to get the regulator to stop changing the voltage first.

When I tried asking around, people said that P2 volvos don't have variable charging voltage, but I am certain this one has.
It doesn't even have more than a positive connection, ground and a blue wire, maybe sense?
But taking off or putting on the blue wire changes nothing.

Can anyone enlighten me on what is happening and how I can make it always charge 14,7V?