I believe I was told that you want to keep the overall resistance down on the older cars. Apparently adding resistors will keep newer more sensitive electronics systems and radio reception better. I honestly don't know if this is true. I've never had any issue with the old or new radios in any of my cars, but I do always try to get hot running non-resistor plugs (NGK bp5es) because I want to burn off the fouling I'm going to get with these older engines that run rich and even burn oil.

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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,