Preheating key

I would like to know how to connect and operation of a preheating and starter key ... and a Veypa 1008-4 contact key

All ignition and starter switches have the following codes: 30 for ignition/heating, 15 for starting, and 0 for ground (or a symbol like a T).

When you turn the ignition on in diesel vehicles, code 30 sends current to a glow plug relay that activates for a few seconds (between 5 and 15 seconds, depending on the manufacturer).