Hello and Welcome -
My name is ***** ***** Im happy to help / advise. Im sorry to see you have had a wait.
The usual cause of this - melted wires, is crossed polarity somewhere- did you get any sparks when re cnnecting the battery etc - modules... If so that can cause this... so long as you rule out the cause of the melted wires.
Further to this... check the earths / grounds - especially the main battery ground circuit - anything bad there can cause what you have.
It could be too as you are summising that the insides of the fuse / relay board has suffered damage - that will cause loss of circuit to your relay there - you will need to strip that open to check and then go from there---with what you find there -
The fuel pump relay is activated from the Ecu - though the fuse / relay board.
Working through as above, you should get through this / sorted,
Let me know how you go..and / or let me know if you need anything further on this..
~~~>>>>>>~ Meanwhile - Please do click on the "Exc / Ok rating" for me at this time.. Thank you in advance for that . ..
Note that you can get back to me anytime at all after doing the rating - it doesn't close you out -
- Best Rgds, MIKE.