Ignition Wire Set
 

My spark plugs were replaced recently (Bosch copper) and I just put in a new Bosch distributor cap and Bosch rotor.

1. How much of a difference do ignition wires make if I were to replace mine in my 1989 300ce? Mine may be the original.

2. What is the life expectancy of wires roughly?

3. What are the best ones to buy Bosch, Beru, FACET etc. ?

plug wires
 

it really isn't the wires that i have had to deal with failing, but the plug wire resistor ends, but at around $29 each for the ends in the long run it is better to buy a wire set. always go with bosch, beru is a good brand, but i have had defective wire sets pretty much out of the box.

Which brand were defective out of the box?

wires
 

it was the beru, the last two defective were on a 300e and a 560, they had come from another shop, or the customer had installed his own wires, the funny thing is that beru is the brand used on some of the newer mercedes engines

Make sure if you are going with Bosch to get them from the Dealer! I have ordered brand new Bosch wires from other sources and got ones where the resistor ends read 1.5KOhms even though they state that they are 1KOhm ones! From the dealer I get 1KOhm from there ends! Yeah they are $30 instead of $10-15 from other sources but they are at least within spec!

Is the resistance measured by inserting one probe into each end of the ignition wire? If so, I measured appx 1,100 k ohms per wire. Is that within spec?

You can measure it at just the connector, but to do a true one you measure from one end of the wire to the other! This will give you total resistance. I have never found anywhere that states what is in spec or not. I assume 100 Ohm's either way should be fine, but I would say they all should match. Right now I have 1000 on one and 1200 on the other three and I have a stightly feelable idle. Not bad and jumping around but noticeable!

This may just be my experience, but I have never once appreciated any operational improvement replacing wires. I know, everyone claims they go bad, and need to be replaced periodically. Others will claim performance improvements with fancy wires or whatever. I have bought fancy wires too, and never noticed any change.

Perhaps I'm just lucky to have not had an actual ignition wire failure...

Good luck.

Most of the times the wires fail due to pulling on them trying to get them out. Or corrosion! Never really saw a wire fail if it was taken care of properly! Mine I had one bad one and replaced them all, end connector came off due to pulling! Not me but someone before me! Now I am just trying to find a good set as it seems that Bosch has some Crap stock that they send to certain suppliers. Seems the Benz Dealers are the only ones to get the supposed good ones.

They do go bad
 

I have had wires go bad. At night, in the dark, you can see the wires arc to the motor or other grounds. I had a light show under the hood.

Beware of aftermarket wires: THe OEM have a threaded end that the stripped wire feeds into. It is crimped onto the end of the wire before the plug cap is screwed on. I bought a set that were made up by a supplier using all OEM Parts, but the ends were not stripped or crimped. They are crap. Even though they are OEM ends and specs, they are not good quality. Save your headaches and buy factory parts or make them up yourself (From factory parts). Next time, that is what I will do.

There are special pliars used to pull the plug boot off the plug.

The Plug Pliers are indispensable.
 

Warren is right. Those plug pliers are critical to keep from pulling the ends off the wire. They will save your hands too. I did it by hand for years (not on Mercedes), but when I bought the SL I decided I needed it and it makes all the difference in the world. I bought one that can be set straight or two angles to the right and left making it 5 positions. Money well spent.

Oh yeah, you want to twist the boot first and twist and pull if they won't come off. Do not bend to the side or you will break off the insulator.

Pulling boots off of plugs!
 

OK, so I've got the special pliers, put them on the boot, twist, and pull like H... and the boots just won't come off! So, what is the trick to get these off? I'm afraid that I'm going to ruin the wires. The last time I changed plugs, I had my dealer do the job 'cause I couldn't get the boots off then either! Any comments would be appreciated.

keep trying, they will come off. The first time I changed plugs on my E420 it was tough getting the wires off. I too, used the tool you have( bought it at Pep boys) and first I just kept twisting the boot back and forth. Finally it cam off with a little tug. I wish I could tell you the "secret" but it just takes patience and keep twisting .

Put a thin film of silicone dielectric grease on the inside of the boots. This will keep them from seizing to the spark plug insulator.

To remove (using the proper tool) twist back and forth with a slight wiggle while pulling away from the head.

Duke