Go in truck - could be rain (7)
I believe the answer is:
urinate
'go' is the definition.
(I've seen this before)
'in truck could be rain' is the wordplay.
'in' is an insertion indicator.
'truck' becomes 'ute' (Australian abbreviation for utility vehicle).
'could be' is an anagram indicator.
'rain' is an anagram of 'rina'.
'ute' going around 'rina' is 'URINATE'.
(Other definitions for urinate that I've seen before include "Pass water" , "use can ..." , "Go" .)