The Thanesar-Kaithal Railway was a branch line of Delhi-Umballa-Kalka Railway(DKR).
Refer to FIBIS Fact File #4: “Research sources for Indian Railways, 1845-1947” - available from the Fibis shop. This Fact File contains invaluable advice on 'Researching ancestors in the UK records of Indian Railways' with particular reference to the India Office Records (IOR) held at the British Library
An on-line search of the IOR records relating to this railway  gives the following: -
- L/F/8/17/1234 “Delhi Umballa Kalka Railway Company, Contract for construction of a branch line from Thanesar to Kaithal; 1909"
- “British Library Archives and Manuscripts Catalogue” - Search; Retrieved 28 Jan 2016
- IOR "Records of the Delhi-Umballa-Kalka Railway Company" IOR/L/AG/46/9"; Retrieved 14 Dec 2015
- Wikipedia Delhi-Kalka line"; Retrieved 14 Dec 2015