Do you have a wiring diagram & can you read/understand it well ? Have you inspected the fuse & relay connectors for overheating ? I know I'm reaching on this one , do you own a I/R camera to check for hotspots or bad connections ?
There are flowcharts to check the wiring or components before you go trying part$ . BTW , a 25a fuse isn't going to bring the world to an end .
This wiring should have been assembled w/ circuit breakers & better relays and relays carrying the loads instead of switches . The bean counters ALWAYS win .