Precision Power PPI4240 - Manual (Page 5)

4
Before beginning, disconnect the negative (-) terminal of the battery prior
to working on the positive (+) terminal to prevent a short to ground.
This is important, unless you want to spend the rest of your life with a
nickname like "Sparky," or "Smokey." Reconnect the negative terminal
only after all connections have been made.
You will need to install an in-line fuse or circuit breaker in the power
wire within 18” of the battery. This fuse or circuit breaker protects your
vehicle from fire in case the power wire shorts to the vehicle body.