1) The diagnostic port is on the passenger side, behind the glove box.

2) The CEL is set only by accumulated mileage - there's a re-set switch on the rear of the instrument cluster.

3) There are about 17 electrical connections between the battery and the starter solenoid switch - all of which can contribute to voltage drop - particularly under load. Common problems other than a bad solenoid switch include the electrical portion of the ignition switch which is easily replaced. Search under my name for installing a secondary relay to send full battery voltage directly to the starter solenoid switch by using a Ford type relay triggered by the original solenoid wiring. The Ford relay will throw with as little as 6 volts without drawing a large load.

4) You need to download the FSM on MontyMcV's site and go through the normal diagnostic trouble-shooting regime.

Frank