What’s everyone using to fuse between the alternator and starter relay

The rule of thumb for fusible links is approximately 4 inches of link type wire two sizes down. For example, on my ammeter bypass I used 8 AWG SAE approved cable from the alternator, and soldered in a 4 inch 12 AWG link.

12 GAUGE FUSIBLE LINK WIRE FOR 8 GAUGE CIRCUIT 2 PACK 9 INCH PIECES - Fusible Link Wire - Fuses & Holders

I just searched for a 8 AWG link wire and did not see anything (you are using 6 AWG, so need a 8 AWG link wire).

If you can clean your breaker with DeOxIt it might help.