On the fuse box...
Panteras have a fuse box produced out of BAKELIT an early "plastic". It is very hard and does not really melt. I suggest you make a Foto on the fuse side, take them all out, get new once and add one by one back in AFTER a full cleaning of the connectors. Even a steam cleaner does help besides mechanical of other chemical cleaning. If connection parts corrode the cross resistance will increase hence it start building up "heat". I kept. my old fuse box but added all new fuses. Modern fuse boxes are more reliable as dif fuse design/blade type.
A switch of a fuse box without a full documented wiring diagram is a killer. As you put fuses one by one back see what the fuse controls and COMPARE the result with the very well documented Pantera wireing diagram / see tech pages. AND DOCUMENT every cable !! Use the pantera diagrams to add the color code and wire gauge to it.
The heavy current is related to (so they are the candidates for "burning")
1) Radiator Fans
2) Headlight and motors. you def convert to H4 so heavy current on the ignition swithc!!!
3) Window motors..
4) honk horn!!! sucks easily 20 amps! if stuck may be 30 plus
You need to rewire these anyways as all current is running via the ignition switch a BAD resign of the old days. All need to set up via new relays. Existing wires serve just a Relay control signals! So keep all in place!
On the Relay panel well, as above take a foto take one by one out and test it. Panteras have this complex relay for the head light motors, I do not see it in your picture. The old relays are good and reliable but can be replaced by modern once 5 USD China stuff/Hella or Bosch. The old type metal housing type is hard to come by and costly. Relays in general nothing wild, simple on off, active on or active off you need to test it. The numbering on the relay connectors are standard so you can easiy figure out that type of relay you deal with. Also new relays optionally work on sockets so you can build a nice socket set up. ..and DOCUMENT what you did
Mat