6. Cylinder duster is now a 340 ignition issues wants to start when you let up on the key
At the moment the only one I can find is this one. I know I have a couple more, but not sure where I filed them.
Some have reported early '75s with seat belt interlock.
As best I can tell, the majority of '75 cars did not.
However they did split the alternator's output power before going through the bulkhead connector.
The power feed to the key switch gets its a fusible link, in addition to the normal fusible link on the battery feed.
Open circles and squares represent connectors.
Solid circles represent welded spices.
Yellow was often used to identify the wire from the key switch to the starter relay.
This may be the 'engine connector'
There's a partial diagram from a '75 service manual
here.