75 duster slant six weak spark

Does that black and red tracer wire splice into the main black or blue wire coming from the alternator as it routes to the bulkhead connector? If so, it and that fusible link is shown in the mymopar.com schematic for your year car. Look at the lower part of sheet A. (Download this if you have not done so already....)

It goes to a red wire on the inside and is the main power feed to the ignition switch in that year. In earlier years, the ignition switch power feed came from the welded splice in the dash harness, but it looks like Mopar fixed changed in 1975 to put the ignition switch power feed from the alternator power output; that reduces the load on the main alternaotr feed back into the ammeter. Soooo keep that in ! You have a 'sort of' Mad Electrical bypass in your '75.