There is a common problem with these starter motors. See this website:
http://repairkitsuk.com/4.html
ChicksFan, July 2013
If it's an electrical lose connection then tighten it up.
If it's a mechanical lose connection - ditto.
You give little indication about the difficulty you have - if for instance you can't find the starter motor then it's on the thick fly-wheel end of the engine - low down usually.
If it's a cable problem just follow the big fat cable from the battery - do not forget that a big fat earth cable will run from the starter motor to the chassis.
A control wire will run to the starter motor relay - check that and its earth return too.
