Although the lamp was only mandatory for trucks,
some used it as a security precaution, in the 80's.
As in an Etsy-Auction (https://www.etsy.com/listing/771657487/varta-warnblinkleuchte-631-oldtimer):
(https://i.etsystatic.com/10635483/r/il/19614f/2205576645/il_680x540.2205576645_bi84.jpg)
The flasher is on the front and the steady light on the side.
It is powered by 5 mono cells, which makes it rather heavy.
In the new times, a friend has put in LED's,
a Li-Ion-Cell and some electronics in between.
Since they do not take as long to light up,
one could shorten the flashing by bridging the middle resistor
of the 5 you see after opening the case, he figured.