Hybrids and electric cars carry a high-voltage system that runs from the battery pack to the motors, the inverter and the charge port. Parts of it sit under the bonnet even on cars that also have a conventional engine, and they are not always where you would expect to find them.
Orange cable is the usual marker, but colour is a convention rather than a guarantee, and a wrapped or repainted loom can hide it. The reliable marker is the label on the component and the layout information for that model, not the colour on its own.
High-voltage cable is thick, heavily insulated and usually run in its own conduit, with connectors that are physically different from the ones used on the low-voltage side. It is built so that a mistake is difficult, not so that a mistake is impossible.
Treat any cable you cannot identify as live. That is not caution for its own sake: the connectors on these systems often carry an interlock, and undoing one without the correct procedure can set a fault that only a diagnostic tool will clear.
Before any work near the system, the car has to be shut down and the high-voltage side isolated according to the maker's procedure for that model. The procedure varies: some cars have a service disconnect, some need the pack isolated through a diagnostic routine.
Isolation is not the same as switching the car off. Capacitors hold charge after the contactors open, and the maker's procedure includes a waiting step for exactly that reason. Follow the sequence in the manual, in order, without shortening the wait.
Most engine-bay fabrication never needs to go near the high-voltage side: an exhaust manifold, a charge pipe on the engine side, a heatshield, an intake for the combustion engine. Those jobs can be done with the system intact, provided the routing keeps clear of it.
Keep drills, saws and hot work away from any cable you have not identified. A nick in the insulation of a high-voltage cable is not something you can tape over, and swarf that finds its way into a connector is a fault that appears much later and somewhere else.
Heat is the specific risk here. Cable that has been close to a welding operation or a heat source can have insulation that looks intact and has lost its properties underneath. Route new pipework so that no cable ends up closer to a heat source than it was to begin with.
When drilling a fresh hole in a panel, check both sides before the bit goes through, and fit a grommet afterwards. A hole that is clear on the side you can see is often not clear on the side you cannot, and that is how a loom gets damaged.
Stop when the work needs the system isolated and you do not have the procedure, when a connector has to come apart, or when a component has to be moved. Those are jobs for a technician trained on that specific system, not for a general fabricator with good intentions.
Our own workshop background is in metalwork and welding rather than in high-voltage systems, so the sensible split is to have the aluminium welding done on the bench and fit the finished part with the system untouched.
