James Thomas Harrison

Just to be sure:

Harrison, James Thomas, 7653 Pte
Born Oswaldtwistle c.1885
Collier
Prior service with 3rd East Lancs [Militia], discharged on joining RWF Regulars
Attested Accrington [Warrington ?] 19/02/1903, age 18, for 3 years with the Colours and 9 with the Reserve
Medical at Burnley 20/02/1903
Approved at Burnley 23/02/1903
Posted 1st Bn, Wrexham, 21/02/1903
Posted 3rd Bn 17/02/1905
To Reserve 01/04/1906
Military character Very good, hardworking
Mobilised 05/08/1914
Posted 3rd Bn 06/08/1914
Posted 2nd Bn 11/09/1914
To UK, posted Depot, date illegible
Discharged Time Expired 18/02/1916, in good health
Attested again under Section D [four years extension of Reserve service]
Demob 05/08/1922
Wife Annie Catherine Harrison; children Ada [1913], Florence Edith [1920], Owen Horace [1922]

As Hywyn already said, his papers are out of focus and barely legible.

John

Wrexham was a large mining community. There were many men from Lancashire living in digs and working in the numerous collieries that surrounded Wrexham. We've had similar research questions involving Lancashire men who enlisted in the regiment pre-1914 in the past. What was your source for the Welsh Guards connection? The guy mentioned by B/Wallah looks a good fit, except for the age. With that in mind, I think you probably need to firm up the birth dates etc. Obtain the following Certificates:

1. Obtain your fathers birth cert. This will confirm your Grandmothers maiden name

2. Obtain your Grandparents Marriage Certificate(this is the crucial one). This will confirm the age of your grandfather at marriage, so indicate a year of birth.

This will at least confirm if he is most likely to be 7654 Harrison. At the moment the forum researchers are giving you information, but unless you research the basic stuff yourself, its all conjecture. Certainly the marriage certificate will be of interest, as it often mentions other family members.
If you need any advice. Just ask.