Join Date: Jul 2011
Location: Cologne, Germany
With the battery switched off (disconnected), check the connections on the starter motor itself are tight and clean, not abraded somewhere and/or shorting.
Check the main starter wire bundle in the connector block on inner fender (driver's side) are also tight.
Is the starter itself tight, are the 3 mounting bolts in place?
If you have the turnoff switch that has a plastic turn knob, these are fairly poorly made, I have had 3 that have just fallen apart, the metal is just some sort of cheap base metal. .....just as a test you could remove it out of the equation and connect the battery cable direct to battery.
Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.