Dear sir,

If your son wants the Amrita main campus then for the ECE branch then it will be going to very tough if your son is not belong to home state category because their major preference is their home state students. You may get end up with not getting any branch here. Your son need to achieve the rank of 6K for the lowest branch in main campus and for ECE he need around 4.5K rank.

JEE percentile won't help him to take admission in Amrita.

Good luck :)