I don't suppose anyone is remotely intested but...
It seems that the only difference between 4 terminal & 3 terminal solenoids is that the extra terminal is connected to the starter terminal via a 3 amp rectifier. The rectifier prevents current flowing the wrong way when cranking the engine.
So, while sourcing a good 4 terminal solenoid, I've connected the starter terminal on my 3 terminal solenoid direct to the coil via a rectifier and it works fine, my temporary switch is now removed.
The rectifier is an IN5404 (Maplins code QL84F) and was horrifically expensive at 52p.
