Hello There Jag fans ! Im New here and into X300 ownership , i have just one problem
and is it whit the battery charging !
New alternator fitted whitc shows 14.6 when im Measure it itself whit the Engine running
New battery as well 100amp -
At the battery terminals the voltage show me is jus 13.1 max But most of the times shows me 12.6 even 11.3
when i switch the headlights on is drop to 10 maybe
What Could be the problem

 

Most likely is a high resistance connection somewhere on the cable back to the battery.

The cable goes Alternator -> Starter Motor -> Lower Bulkhead -> Mega Fuse -> Battery

Check the connections at each point for corrosion and tightness. First two are the most likely. If you have a multimeter and long leads you can do a voltage drop test along the cable to identify the problem area.