Dash harness replacement and upgrade.

Easiest is put both red & blk leads on the same ammeter terminal. In addition, you can run a ~6 awg bypass wire from alt+ to Batt+ (or starter relay stud). That will keep the large battery recharge current out of the cabin. Search "MAD Bypass".

Several of us here installed an underhood relay/fuse box from a later vehicle. See my "Modernized Engine Wiring ..." thread, where I used one from a 95-99 Jeep. Or you can buy a new $$$ aftermarket one. Either way, you must customize the wiring. 2000+ cars tended to use boxes w/ connectors that might be harder to retrofit.