Question

in business letters, are lines to be left between thanking you, yours truly and name?

Answer 1

No.. in none of the formal letters

Answer 2

Lines should be left between the last Paragraph of the letter body and thanking you

And between thanking you and yours sincerely also line should be left

But line should not be left between yours sincerely and name

E.g.:-

_ _ _ _ _ _ _ _ _

Thanking you

Yours sincerely,

Name.