Hello and Welcome to justanswer...
When this happens, you will see / note that the Led for the alarm / immobilser system will flash in sequences - rather than its normal slow pulse mode... thats if the fault is immobilser system related.
So check for that - and if you note it doing so, carefully count the flashes. It takes a bit of getting used to - but you will see the sequence - it will be, example - one flash, then a pause - then two..or three or more and so on -making a fault code... ie, one flash then 3 is code 13.. and so on. If you find it doing that , you can let me know and I can tell you what the code is/ where the fault is.
I can tell you however, that very often on this model, you will find that happening with the light, but there were common causes. One was the wiring to the injection pump - check very carefully for chaffed wiring there - and on the loom to it ( check it through) - but check very carefully to the connectors - the large connector on the loom to above the pump ..sometimes just disc / reconnecting this would cure a bad connection - but a spray with switch / contact cleaner is often needed - ( do not use wd40 as it will short the contacts)
Other than that - follow the starter motor wiring - often you will get a chaffed / damaged wire on that circuit - and that will cause you exactly the same issues.
The only other way would be to have the system fault code read when it does this - either at a local garage or have a mobile mech with equipment to it do that when it plays up ... but working through as above will normally have this sorted.... they are common faults with these models.
Im very pleased to have helped you - Let me know if I can help anymore...
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Kind Rgds - MIKE