The foot switch is a normally open switch witch can be placed at the co-pilote to reset the trip distance. Also any other Normally open momentary switch can be used for this purpose. It is also possible to have more than 1 switch in parallel to relieve your feet at certain stages.The footswitch is usually used in speed rally cars where a foot rest is placed and a hole can be drilled into that. A foot switch is more robust and easily and more robust installed in the car. And take it from me, althoug hyou think it is small, you do not miss when you want to push it.
For the foot switch you only have to connect 1 wire to the tripmaster. The other wire goes to the ground of your car (can be done in the tripmaster ofcourse but is not preffered due to the amount of wires).
All external switches in our system are always switched to the ground: This only gives the need for 1 wire and if the wire is damaged and comes in contact with your car, you will only get a strange readout but not electrical short circuit will happen..