There's a great example I found a while back when I replaced the fuse box in one of my Range Rovers. It has seven plugs (there's space for eight) each of which

There's a great example I found a while back when I replaced the fuse box in one of my Range Rovers. It has seven plugs (there's space for eight) each of which have space for eight pins. The plugs are identical - almost. They're different colours, and they have a T- or U-shaped pin that fits into a hole in the appropriate flying socket on the engine bay wiring harness. The pins are rotated for each plug. [1] There's no way to fit the fusebox the wrong way round in the engine bay because it has three mounting holes with odd spacings, and one has an angled slot for a bracket that holds a coolant pipe which definitely wouldn't fit if it was wrong. There's no way to fit the sockets in wrong even without the pegs because the wiring harness only allows them to line up with the correct plugs. Even the three high-current screw terminals that feed the body ECU under the driver's seat have got little lugs sticking out so you can't mix them up, although since they're all unswitched feeds fused at 60A it kind of doesn't matter. There are a lot of nice little bits of design like that. Shame they didn't extend that to the ignition coil connectors on later V8s, which are the same for both pairs of coil packs. See if you can guess what causes a lot of "crank, no start" faults when people have been in at the back of the engine. [1] https://bparts-eu.s3-eu-west-1.amazonaws.com/images/62538/big/bo8uaeq7xw6vucxhwnx4jv31letfda3i.jpg https://bparts-eu.s3-eu-west-1.amazonaws.com/images/62538/bi...