Path Pro Golfstore

I bought an Inductive Craftsman Timing Light (Non Dial Type just basic). All wires form into a electrical plug that goes into timing light. One Wire has a little clamp to be hooked on to the #1 Ignition Wire ( Close as possible to the spark plug boot) . The other two wires consist of a red clamp and a blk clamp .

The manual it states 2 different ways to hook up B&R Clamps.

Positive Ground Systems - Says place blk clamp on (-) Terminal on Battery and place red clamp on a ground (They suggest alternator bracket or engine block)

Negative Ground Systems - Says place red clamp on (+) Terminal on Battery and place blk clamp on a ground....

Im almost positive that my car is a Negative Ground because off the (-) terminal, there is a wire that is secured down to the engine frame. Am i correct on this?

The manual states dont hook blk clamp to (-) term and red to(+). Why is this? Whats a good spot on engine block for ground?