He will not be at Wigan or Ashton if he was in the Militia, The Militia records are at the National Archives, for the Manchester Regiment Militia Battalions 3,4,5 & 6
WO96 Militia Attestation.
They range in date from 1806-1915( I have not found any yet with a date later then 1908).
You would need to look at WO96/991 (Brow-BUR), they are not on line yet so you would need to go to the NA yourself or get a researcher to look for you.