fusible link question

Agree.
There is a small chance your '75 has a heavy duty wiring arrangement that has a fusible link in that location. Such an arrangement is shown in an earlier service manual for b-bodies to protect the 8 gage wires There will then be a second fusible link to protect the 12 gage wires.

1975 can be a little confusing. A standard '75 has one 16 gage fusible link between the junction on the starter relay and the firewall connector. It has a second fusible link on the branch from the alterator output wire to the key switch.
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If the car was equiped with heavy duty alternator and/or rear window defroster grid, then its a bit different and you may find a fusible link attached at the starter relay. It still protects the segment going to the firewall, but instead of going to the multiconnector the next segment goes through a grommet.

Some photos of '75 and more wiring diagram info in this thread
https://www.forabodiesonly.com/mopa...-you-let-up-on-the-key.544566/post-1974370034