Hello
The reason is called "Funkfernentstörung".
Since the 50´s all cars must pass the german DIN 59 879/VDE 0879.
I think comparable to the MIL-STD 461/462.
One thing on the 73 RS was that the cars failed the test and Porsche had many trouble geting the car street legal in germany.
To pass that the cars where officialy sold with the standard lid and then the costumer ordered the Bürzel seperatly as "Zubehör". Some Bürzel had a Steelframe and a fine mesh in the laminat but had only seen one of those at a company done the race ignition development for Bosch. In 1974 the Bürzel get a shielding sheet inside.
Radio supression is very important in europa as many bands whern´t usable for the puplic ( Well germans had to use FM for the Radio by the lack of frequencys ) and well its a small country.
The HKZ can generate very high radiation output if the system is negletet.
The groundstraps must have very low resistance and are made from OFC.
BTW Porsche Weissach is one of the leading companys in EMV
Grüsse
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