Hoping someone can help here!

My ancestor, John Whitmore Garrad, was born 5 Nov 1827 in Colchester, Essex.
He died in 1897, back in Colchester.

Sometime after the 1851 census, he signed up with the Bengal Army, 9th Regiment Light Cavalry.

I have found 2 mentions in the East India Register & Army List 1855.

The only other mention I can find is in the Indian Army & Civil Service List 1873, where he is at the Bengal Stud Establishment.

I cannot find any references in Army Pension Records, or indeed any other military records.

So, how can I find further details of his military career?

Kevin