[Healeys] Starting (cut off switch)

[Pieter and Linda]

Listers,
 My car has a modern high ratio starter and usually starts first time. A
couple of weeks ago the car was parked for about an hour after a run and when
I went to start it, I got nothing but a click from the starter motor. After a
bit of a general tightening of connections(none of which appeared to be loose)
and switching the cut off switch back and forth of  the car started as normal.
It hasn't happened for a few weeks but, today, whilst in the cue for the
annual roadworthy ( MOT/TUV) inspection the same thing happened. Quite
embarrassing. This time however there was a jump start pack available and the
car started fine with this connected and has started on it's own about 15
times since. Since I cannot find a loose or corroded connection, the battery
is good and the leads are thick copper and in good condition I am starting to
suspect a faulty cut off switch. Is it possible that there is corrosion in the
switch that the normal battery power can't get passed but with a jump battery
connected in gets through. Any suggestions before I ditch the current switch
and fork out for a new one.
 Incidently the car failed it's check. Not because of the stating issue but
because of a small area of abrasion on the left front brake flexline. You
can't say these inspections aren't thorough :(

cheers
Pieter