As WOW suggests the solenoid
could be on its way out
I have a test to see if it is jammed

First make sure the vehicle is in neutral
(Ignition OFF) There are 2 thick cables which terminate with
rubber caps one from the battery the other to the Starter OK?
Get a metal object (old screwdriver with an Insulated handle is ideal) raise both the
caps and bridge (dab) the exposed terminals with your "tester" You'll probably get a
large spark/arc and the starter motor will turn over
If this happens the Solenoid is OK replace the caps and look elsewhere
Don't leave your tester in situ! The Amperage is sufficient to weld it to the terminals

(hence the "quick dab")
If its a preengaged starter and the solenoid is faulty then the entire unit must be
replaced

But good news there are car electrical workshops who will part exchange it for a
reconditioned unit

Official dealers will only sell you a brand new unit

(not interested in exchanges)
Option 3 is to locate a unit at a Wreckers yard(Cheapest way) but there is no
guarantee that it is good (have to take their word for it) also there is no money back if
its unsuitable or defective.

They'll let you test it before leaving, so bring a battery and
some battery leads along with you run the test as above.Also bring along a knowledgeable friend if you can? So they cannot Flim-Flam you!
