I would like to know what king of signal is on TF socket on a W124 260E 1988, euro, on the fuel pump remay?

It is said that if theTF signal (RPM) is missing for 1 sec then it cuts the fuel delivery.

Is it a continuous voltage, a pulsed signal, or something else?

Thanks for help

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Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class, 220CDI, 2009, W204

Sold: E-class 260E, 1988, W124, Wonderfull car sold after 489 000 kilometres of reliable services (engine M103, clutch, brake system and 5 speed manual gear box all original).

Sold: E-class, 320CDI, W210, 2000, 225 000km