the hood pin switch is a plunger style switch that opens a circuit when the plunger is compressed (hood closed), and closes a circuit when the plunger is extended (hood open).
the hood pin is mounted in a hole under the hood along the rim of the engine bay. It has to be in a spot where the edge of the hood will cause the plunger of the hood pin to collapse when the hood is shut. The hood pin has to be in contact with metal to complete the circuit when the hood is open. On the end of the pin you can insert a bullet or female wire connector.
This wire can then be connected to pin 6 of the black 10 pin harness of the db-all, which is an input wire. When this input wire is connected to ground (through the hood pin switch or toggle switch), this will cause the db-all to not initiate a start sequence.
The "neutral safety switch" is a toggle switch that can be mounted anywhere you want and connected to ground on one side, and the same wire as the hood pin switch on the other. Turning the switch on is effectively sending wire 6 of the black 10 pin harness to ground. You can think of this as an on/off type switch for the rs.
As a side note: If you ever read of a neutral safety switch in a car, it typically means a switch that is connected in a way to show the car is actually in neutral, and can safely be started. What they are calling a "neutral safety switch" would really be a "safety switch" instead. Just a little fyi in case anyone ever gets confused.
Here is a link to the install manual of the db-all. It shows where the wire is located that needs to be hooked up.