I'm almost reluctant to even start on this topic again, but I've read so many threads here and at MBCA that I'm no longer sure I know anything about the correct plugs to use on my M103 motor. Here's my starting point:
1) Almost everyone says non-resistor plugs b/c of the resistance already built into the plug wires and cap;
2) EPC lists Beru, Bosch and Champion numbers, all non-resistor types;
3) WIS says that MBz no longer approves platinum plugs;
4) Many enthusiasts swear by NGK plugs.
So I did a cross-reference check using the Bosch H9DCO part number from the EPC to ID the correct NGK plug, and it coded to TR5. But the NGK website says TR5 is a resistor plug. Numerous posters have said that they ordered H9DCO plugs and HR9DC plugs were substituted by the vendor. Some other posters say they regularly use platinum plugs and like them better than copper.
I guess the easiest thing to do is to just go the dealership and let them supply me with the plugs they have and not worry about it, but I'd really like to know why there is such a debate raging over something that seems like it ought to be one thing or the other. But which one...??

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't