start lockout switch 300SE

I have a 300SE 1993 3200cc Petrol and recently when I try to start with the key it will not activate the starter although the gear lever is in the Park
position, then when it does eventually start It will not let me remove the key. I suspect it is the start lockout swich or a faulty relay. Can you tell me where to locate the switch and relay. Many thanks Dan
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