As I can't find a wiring diagram for my '86 2.8i Capri, can anyone please tell me what the small (about 1 inch x 1 inch x 1/4 inch thick), black item is that's screwed to the top front offside of the engine bay and connected to the battery negative terminal and also into the wiring loom. It's got 'Ford' moulded into its upper surface. A previous owner has cut into the lead to add what looks like wiring for an alarm system but that's long gone. I've got to tidy the wiring up but it would be best if I knew what that bit does.