For a technician working on a car, what is one critical rule when disconnecting connectors with the ignition on?

When working on a vehicle with the ignition on, one of the most critical safety rules is to disconnect the battery first. This is important because maintaining an electrical connection can create hazards, such as accidental shorts or energizing components unexpectedly. Disconnecting the battery serves as a precautionary measure to interrupt the electrical circuit, reducing the risk of electric shock or damage to the vehicle's electronic systems while a technician is working. This practice helps avoid potential injuries and protects both the technician and the vehicle from harm caused by inadvertently activating circuits or components.

Using protective eyewear is certainly advisable when working on vehicles, but it's a general safety precaution rather than a specific rule for electrical work. Not using a ground strap or ensuring there is no voltage present may address other concerns, but they do not provide the same level of immediate safety regarding the battery connection. In summary, disconnecting the battery first is the most critical step to ensure safety and prevent electrical issues when working on a vehicle with the ignition on.