The heater matrix started to leak so i bypassed it.
What sort of job is it to change?
Also the battery lights comes on at idle but goes off around 1500rpm.
What is the best way to access the alternator as i cannot see it from the top
Any advice would be appreciated

Hi can't help with the matrix but you will get to the alternator easier if you take the drivers front wheel off,still not brilliant access but a lot better.

Check the belt is tight.
Excellent post here for the matrix, there are a choice of two or three for the 1.9, mine was the dearest when I took it out.
https://www.fiatforum.com/ducato/191903-dashboard-removal-heater-matrix.html?p=2072162

It did go back in eventually, there was a screw or two I just couldn't get back in, and even more skin lost.