*I started this job partway through, I was contracting to another workshop.*
The battery went flat overnight, the customer pulled it out to charge, then put it back in; smoke started coming from the engine area so the customer took the battery back out and got it towed to a local workshop.

Car starts and runs fine. Thermofans constantly on (when Integration Relay is fitted), none of the other components the Integration Relay controlled worked (rear demister, fog lights, high beams), and the Integration Relay gets extremely hot.