Well this is pretty cringeworthy, but I didn't have much of a choice. Cut a hole in the floor pan above the fuel sender unit and pulled it out. I have no idea why the manufacturer couldn't put a bloody access hole there in the first place! I'll be patching it up nicely with sheet metal and silicone. Anyway.. As expected the fuel pump has drawn too much current before failure and has melted the power wires within the connector to the point where they've come together and shorted out. Looks like a complete sender unit is in order!