Final answer:
When removing a battery from a diesel engine, it is best to disconnect the negative terminal first to prevent sparking and minimize the risk of electric shock or damage.
Step-by-step explanation:
When removing a battery from a diesel engine, it is recommended to disconnect the negative terminal first, followed by the positive terminal. This is done to minimize the risk of short-circuiting or sparking that could lead to accidental electric shock or damage to the electrical system. By removing the negative terminal first, you break the circuit and eliminate the possibility of a spark occurring when you disconnect the positive terminal.