The whole electrical system in the Delorean leaves much room for improvement. Typically there is a fusible link to prevent this kind of thing. The whole ground side is "missing" and should have it's own dedicated harness. Because this was done by Lucas, they like to switch the ground side of things as opposed to everyone else who switches the positive or HOT side. By switching on the ground side there are many more ways you can have problems. By not having a good grounding system, backfeeds can cause all kinds of weird, hard to troubleshoot, problems. Many circuits are wired with wires too light for the current they carry. I can go on but you get the idea. One way to prevent this kind of thing is a yearly inspection. Good thing you had a master switch so you could quickly shut things off!