First off from what you are describing " across the negative terminal to the negative battery cable" is meaningless as someone already stated. But that's another discussion.

The "seat back arrester" only applyies to coupes, the "warning monitor" is a relay type box located under the driver's side dash, above and on the passenger side of the parking brake foot pedal. The module has connections to the Key warning buzzer, the headlight buzzer, set belt warning indicator, brake fluid level switches, driver's door switch, the "blue exciter wire to the alternator and a few other inputs, outputs and ground.

"Hazard Warning System" is the emergency or four way blinker system.

I can't find anything about "diagnostic".

If you could determine the current flow between the battery negative terminal and ground that would give an idea as to how much power was flowing and in doing so draining the battery. The amount of the drain might give a better idea as to what is actually consuming or draining away any current flow.