Look for the cylindrical splice as shown in the center of this photo. The fusible part is from that splice to the ring terminal. As Matt pointed out, the fusible link may be either attached to the stud on the horn relay or to the battery terminal on the starter.

 

^^^X2 ^^^ Joe's pics really help here !!
My 76 Olds 350 has 2 fusible links . I believe your 73 will have both as well.
A brown/red wire running from the starter solenoid to the horn relay, another (RED) from the horn relay to the fuse panel.