I own a 1991 420SEL with 188K miles on the odometer. The car runs fine, except for a little occasional rough idle. All components check out fine, so I think that maybe after nearly 200K it is time to replace the spark plug wires, which are still the original ones. Any suggestions on what wires to get? should I get OEM wires, or maybe some performaces ones, like ACCEL? the second part of my question is: How difficult is it to replace the spark plug wires on a 420SEL. I've done the job on other cars, but somehow M-Bs seem more "intimidating." I'd appreciate any and all suggestions. Thanks.

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OE wires & ends made bu BERU are the best! Not at all difficult to install!

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Stay away from aftermarket wire sets(like ACCEL). Besides looking just plain goofy(in my opinion), they have way too much resistance. American and European cars differ in ignition system design.
Regards,
Randy D.

What about Magnecor wire sets?? I already posted this over in Tech. Haven't gotten any answers. Didn't realize this was going over here.

I bought and installed Magnecor 7mm wire set on my 85 300E and have had no problems.

Was I mis-informed when local sources tried to sway me towards factory wires? I was told the metal around the boot (at the spark plug end) was a resistor that was needed for "proper spark characteristics"?

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I have been using Bekker's 8mm wires on my 500 SEL for the last two years without any problems. The wires came with OE Beru connectors. My car was noticably smoother with the new wires.

I've heard of Bekker's 8 mm set. Sounds interesting!
What were you experiencing before the switch??

Nothing. The car ran fine before the switch. I just wanted to see if an improvement could be made. After the switch the car idle a touch smoother and much smoother at high RPM. I have not desire to return to OE after this experience.

I use 8mm on my Porsche and they made a difference also. Porsche is known to have the best stock ignition system but even that can be improved upon on.

The concept of Benz having the resistors on the end of solid core wires is that all wires, regardless of length,
are electricaly uniform. The resistance on the other end is built into the rotor and is , again, common to all plugs.
Whereas, Resistance wire ohmage is measured, and increases, with length.
So one plug, being fed from the same coil, can have a much higher resistance circuit than another with a shorter wire.
The solid core wires also last much longer.
Another reason not to use resistor plugs.