Day service detailed, guide on the way (6)
I believe the answer is:
satnav
'guide on the way' is the definition.
(navigational guide used on the way to a place)
'day service detailed' is the wordplay.
'day' becomes 'sat' (abbreviation for Saturday).
'service' becomes 'navy' (navy is a kind of service).
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'navy' with its last letter taken away is 'nav'.
'sat'+'nav'='SATNAV'
(Other definitions for satnav that I've seen before include "Driver's route finder" , "Device for finding one's way" , "Road atlas replacer" , "Route guide" , "Talking road map?" .)