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Courtesy of Craig in Davis
Proper functioning of the ignition system is paramount to a good running car. Replacing the ignition wires is a simple, inexpensive and easy to do repair that can make a world of difference. The OEM ignition wires have “screw on” terminals at both ends of the wire. The wire itself is copper stranded ignition wire 7mm diameter. You can purchase a full set of ignition wires with terminals or simply replace the old worn out wire and reuse the terminals
With the stock ignition system the spark plug terminal and the distributor terminal ends have internal resistors. The wire itself is a conductor but not a resistor. Proper resistance is important for optimum function so you must use the OEM wire ends with non resistor type wire.
To replace the wire, first remove the distributor cap, spark plug wire loom and coil wire. Inspect the terminal ends for corrosion, cracking, or other damage. This is a good time to degrease the terminals to facilitate inspection and to help make the engine compartment look spiffy. If any terminal ends are damaged they must be replaced. Next, open the plastic wire guide to allow individual wire placement. Remove one wire at a time by unscrewing the spark plug connector then threading the wire out of the plastic wire guide. Then unscrew the distributor terminal end. Measure the wire and cut a new section the same length. Screw the distributor terminal end back onto the new section of wire, thread it into place in the plastic wire guide and screw on the spark plug terminal. Repeat this procedure for the remaining wires. (Editors note: Mike W adds: "I would ohm-out the connectors with ohmmeter before you reinstall them. I have had them fail open electrically, but pass visual inspection.")
The pictures above are from left to right, the distributor end terminal and some ignition wire, ignition wire and both end terminals, spark plug terminal spark plug wire end, and spark plug terminal spark plug end. Click on images larger versions.
Shown below is a distributor end resistor connector and spark plug end resistance measurement with ohmmeter, both courtesy of Mike W. Click on images larger versions. Mike reports: "Resistance is about 1.6K on the spark plug connector itself, but they should all be relatively close, say within 10% or so. On some cars, I think the correct spark plug cables for 528i's, they have an additional resistor at the distributor end. I measured it at about 1.2K. And the rotor should be 5K. If the cable end looks like the one pictured, it has a resistor in it. Some are removeable, but most aren't."
I purchased replacement ignition wire at NAPA auto parts for $0.51/foot back on October 2004. I purchased 15 feet of bulk copper core wire which was just enough so you may want to get 20 feet to have a little leeway in your measurements. Some stores will only sell the entire reel of 50 or 100 feet but the one local to my work would sell it by the foot. I used 7mm diameter which worked fine, I think 8mm will fit but will be a snug fit inside the connectors. Check the fit before you buy a reel.
NAPA has bulk wire available at the local store only it isn't available online but you can view the specs online. NAPA part numbers BEL 734705 yellow 8mm 50 foot reel, BEL 734706 blue 8mm 100 foot reel, BEL 734708 white 7mm 100 foot, and BEL 734803 black 7mm 100 foot reel. I used the BEL 734803 when I replaced my wires.
I checked online and found that Summit Racing sells Accel copper core wire in bulk quantity in both 7mm and 8mm. The part number for the 7mm wire is ACC-160090 and cost is $71.39 plus shipping for a 100 foot reel. The part number for the 8mm wire is ACC-160092 and cost $77.99 plus shipping for a 75 foot reel. Prices and links are effective September 2006. In addition, Kingborne makes copper core wire.
If you can't purchase just the amount of wire you need then may I suggest an E12 wrenchfest. Wrenchfest is a term I picked up over on MyE28.com but I think it is ok to use here. Basically, it is a get-together to work on cars, eat, drink and socialize. Purchase 100 feet of bulk wire and replace the plug wires on 5 or 6 cars.
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