130T2 should have the same setup as the AS350 series however I do not have the manuals at the moment to reference. Once the main rotor starts turning and gets the MRGB above 1 bar of pressure the MRGB pressure light goes out, that same signal that turned the light out also sends 24 volts to one side of the hobbs meter.
Then under the floor of the aircraft, on the flight control tube that connects between the pilot and co-pilot collective, a small metal tang is activates a microswitch once the collective lifts appx 1/2''. This switch is feed with a ground signal from a nearby grounding block. The switch while it only has 2 positions depressed or undepressed has 3 electrical tabs where a 1/4 push on spade connector can be attached. Lets call them Common, tab A and tab B.
The common is fed a ground by the grounding block nearby. The other two are for using the switch as a normally open or normally closed switch. If you hook up to tab A this means that with the collective in the down position, the microswitch is being depressed and as a result no ground signal is leaving the switch to go to the hobbs meter, without a ground the hobbs meter does not run. Once you raise the collective the switch is undepressed and the ground signal is allowed to flow to the hobbs meter and then it begins to run.
If you hooked up to tab B it works in the opposite direction. With the collective down the microswitch sends the ground signal through to the wire that is hooked up to tab B. Once you raise the collective it breaks this connection and you no longer have a ground signal. This is normally used to connect to a garmin transponder, traffic device or ADSB component as it has inputs for squat switches. This is how it determines if the aircraft is on the ground or in the air for purposes of changing your ADSB symbol, it can run the flight timer clock on the GTX series transponders and a host of other items.
Which one of this tabs you tie in with for the aftermarket equipment is based on what they want to see. Some avionics when given a signal whether its voltage or ground think the aircraft is on the ground and the removal of the signal means its flying. Other companies its the other way around.