I am going to fit an isolator for use when the car is parked up but I don't know whether to go for a simple switch in the fuse box feed or an FIA isolator as I've been told the ECU learns, adjusts and stores it's map over time so disconnecting the supply would wipe the memory.

Anyone know whether this is true?

If it is I'll keep the cable from alternator to starter to battery and the permanent live from battery to Ford EEC-IV and just fit an isolator between battery and fuse box.

Otherwise I will go for the FIA one with the spade terminals on the bottom - If I went this route, would I feed the ecu and fuel pump relays from the coil spade terminal underneath or the large main loom ring terminal?

Also, do the starter, alternator and fuse box connect to the large ring terminal?

For use as a security device just put an inline fuse holder with a 2 amp fuse to bridge the connector studs of the master switch, if anybody tries to start the car without turning on the switch the fuse will blow.

I'm not bothered about the security aspect, I just want a single off swith for the electrical system so I don't have to remove the battery to work on it and so I can leave it in the knowledge that it shouldn't burn to a crisp.