You are probably correct that your fans have a common fuse. It would be worthwhile to rewire the relays to have separate fused path. Pull power directly from the battery with inline fuses and avoid the ancient fuse panel altogether.
Check that your fans are free spinning and not hanging up on something, or have internal friction. Also make sure your alternator & battery is tip top and is putting out 12+ volts. When voltage drops, then the current a device draws increases, and could max out the fuse.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.