Help... defender td5 new Alternator not charging

Hello
My td5 was not charging the battery so I replaced the alternator for a new one but when I started the land rover the battery was not charging anyway so I took the two alternator to be professionally tested and they are booth at 13.5 volts, but in the car cant get more than 12 or 11 volts sometimes. Can anyone help me how to troubleshot this

Thanks
Here's a pic of my defender
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might help,

check this link.
https://www.landyzone.co.uk/land-rover/help-alternator-trouble.257054/#post-3062717

Cheers