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Sparkplug Wires

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The original wire sets on these cars used black wires an had ends which could be removed and replaced. The original spark plug wires were stranded solid copper and failed only when the insulation deteriorated or the resistor ends went bad. These original sets were easily repaired. Bulk spark plug wire could be ordered by the meter and the ends simply could be screwed on preserving the original look of the ignition system. The resistor ends could be ordered and replaced if they failed. There are many over 100,000 mile cars with the original wires still going strong.

230SL, 250SL, original 280SL

JA17 has maintained the below 280SL for the last 35 years and know the wire set to be original. Periodically some of the wire ends were replaced with what is available new or used.

Beru wire set

As far as wire routing some engines had the spark plug wires below the injector lines and some had it above. There seems to be conflicting information on this fact with photos available showing it both ways. Look in the BBB you will probably see both. One fact is for certain, if the engine came with the plastic moisture cover over the distributor, the wires had to be routed below the injector lines.

The 230SL used the metal tube to hold the spark plug wires. The 250 and 280 injected engines did have a plastic sleeve around the spark plug wires where they passed over/under the injector lines.

Original wire sets had removable ends.

280SL with transistorised ignitions

Although we are not sure when everything changed, however the metal shielded 5K ohm resistor wire ends were used on the factory cars with the factory electronic ignitions which delivered a higher voltage at the spark plugs.

If you have the original wire sets, the early pre-transistorized use a 1,000 ohm resistor at the spark plug end and the later transistorized version use a 5,000 ohm resistor. These wire sets have resistors at the distributor end also. The easiest way to check is to meter each wire and check it against the others, any one which is significantly lower than the others should be checked further to see which end is bad. Remove the distributor cap with spark plug wires and check the entire run from inside the distributor cap and through the spark plug connector one at a time. Mark the spark plug ends if you are unsure on how to re-install the wires at the spark plugs.

Below is a 1969 280SL with factory electronic ignition. It has the 5k ohm spark plug ends and the 1k ohm distributor ends.

Late 280SL

Dr Benz disagrees here: "The only wire sets worth putting on the car should only be 1K ohm plug ends and NO resistors at the cap. The 5K ohm ends aren't even used on 560SL's, why would you want to use them on a car with less voltage in the ignition system than a 560? Note: don't use wires with carbon core or you will have very bad running conditions, rich running, rough idle, hard starting and poor mileage. Carbon core wires have too much resistance for ignition systems with only 13,000 - 18,000 volts.


Start every tune-up by measuring the resistance of each original spark plug wire. If the original plug wires sets are still on the car check them and replace the resistor ends or cables as needed. Once the original sets are gone the engine bay will never look the same. Too often replacement sets are different colors and configurations. Generic sets may not have the correct cable lengths or correct ends.

Link to related components where appropriate.

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Joe Alexander: the original spark plug wires are solid copper and very rarely go bad. However the screw-on spark plug ends have built in resistance and these do go bad. chances are if you replace the whole set, you will never get another set that looks as good or lasts as long as the originals. I advise that you check each wire and replace the bad ends. Finding original ends may be a challenge, but I am sure some listers have spares. Make sure you still have the original solid copper wire and that it has not been replaced by those troublesome carbon resistance wires.

If you do have some damaged plug wires, original solid copper plug wire is still available from some motorcycle and farm tractor sources. I remember JC Whitney used to sell it by the roll. I usually check all my plug wires and ends with an ohmeter during a standard tune-up. Mercedes used several versions of wire ends during the 113 years. Same vintage Mercedes sedans used the same in many instances and are good parts donors! The coil wire was also solid copper originally, and had a screw-on resistance end. I am not sure what the spec. for it is but I can dig it up if needed. I have seen a lot of beautiful original wire sets discarded just because of a defective end! I would change only as last resort if your concerned about original appearance.

The original Beru spark plug wires are hard to come by (I have been looking here in Germany for several years and have never found them). However, if you order a new set from Beru, you will see that the metal 'ends' screw into the wire, just as the original bakelite ones did. I simply transferred my bakelite parts on to the new wires and achieved (albeit not cheaply) a more or less orignal look. From time to time, I see the Beru bakelite parts at auto shows here.

Question: I need to change the spark plug wires on my 1965 230 SL. I cannot get originals. I have the original wires. Has anyone had any experience in buying 7 mm suppresser cable and using the original Bakelite ends that attach to the spark plugs? Is there a trick to attaching the new wire to the old Bakelite ends?

You do not want supressor wire. The original use the resistor ends and the wires are solid copper wire core. Get some good solid wire, cut to length, and then screw it into the ends. Pretty simple. I have used different brands and like Beru or Packard, but there are others. Speed Shops have it by the foot.

Question: I am changing the spark plug wires on my 230 SL. I am using copper core cable and it comes with an attached boot. The original bakelite boot has a resistance value of 1K ohms. How important is this original boot and it's built-in resistance of approximately 1K ohms?

For the first six months I had problems with my 230 SL cutting out. I had put in new plugs, wires, points, coil, had the tank cleaned out, changed all of the filters, etc. The spark plugs were always fouled. I turned the fuel injection pump back, installed hotter spark plugs, and trouble-shot all of the cold start / warm-up systems. The car ran decent enough but the plugs were still fouling.

I checked the timing chain stretch, reset the timing and still the plugs looked the same. On talking this all over with a knowledgeable friend we agreed that I should look at the strength of the spark. Low and behold turned out I had the wrong spark plug wires. They were of the suppresser filament type and had resistance readings in the thousands. I removed them and installed solid copper core wires. Now my spark plugs have a beautiful brown ash colour. The car runs like a young colt.

I was able to get a factory set of spark plug wires but could not get a coil wire except if I wanted a 1971 coil wire from the later version. Is there a source for factory ignition wires? I understand the original ones were made by Beru of Germany. I contacted their distributor KingBorne in San Macros, CA and asked them if they could match up the factory wires by sending them a sample. They did not have the same wire. They have a silicone core wire.

Pete Lesler: the early, pre-transistorized ignition cars already had bakelite resistor terminals installed rated at 1K ohms, the steel resistor ends starting with the transistorized ignition was rated at 5K ohms. Donít use resistance plugs or silicon resistance impregnated wire. Use of one or both will materially reduce the intensity of the spark. You may be forced to make up your own plug wires with solid copper core spark plug cable. I have used Packard 440 cable in the past. The terminations screw into the copper core and the ends that plug into your distributor are available as a kit as is the cable from almost any good auto parts supplier.

SL-tech sells a repro set of ignition wires on their website.

Dan Caron says: be careful when buying ignition wires. The 230 SL uses wires with bakelite ends. K&K's wires are correct and is what I use and sell. Some are made by Beru but they are still correct. Stay away from any wires that have carbon core in them. All wires should have the 1K ohm spark plug ends and the best ones don't have any resistors at the distributor cap. I prefer the 230 SL wires over almost anything else. I also use the 26KV coil with a 1.8 ohm balast resistor. Very good set up.

What you want is really low impedance wires so all the spark can get to the plugs. The standard black coil used on some early cars is only 13,000 volts , the blue ones are around 20,000 volts and the hottest standard coil is rated at 26,000 volts. This is the one I convert to. You need to use the 1.8 ohm balast or twice what the black coil uses which is .9. Total package with Bosch wires runs about $160 for all the parts you need.

Question: I have noticed that my engine has a slight (very slight) stumble at idle. I checked the wires and my number 1 spark plug wire reads 5,000 ohms-should be 1,000 to 2,000, so I will replace all the wires just to have a fresh set. The wire between the coil and distributor cap reads 10,000 ohms. Does anyone know if this is correct? Is the resistance supposed to be this high for radio noise supression?

I'll be interested to hear when you track down the cause of the stumble, because I have also have a rough idle which has proven to be very stubborn. Like you, for some reason I had a 5K connector on the number one spark plug. Thinking I had found the cause of the rough idle, I changed it to 1K and later replaced the entire set of wires. This resulted in no improvement at idle. I have since learned that spark plug wires rarely cause problems on these cars.

Never just pull spark plug wires straight off; but rotate the sleeve slightly and they'll remove much easier. This is especially true if the plugs have been in for a while, you need to break the rubber seal.

Question: This may sound like a real silly question. But I can not find the answer in the BBB. The firing order of our w113 engines for the cylinders is 1-5-3-6-2-4 (as casted on the valve cover) and in clockwise direction (as you look down into the distributor). Question is which post on the distributor cape is the #1 ? The replacement distributor on my 71 280SL does not have the marking.

If you take off the cap, there is a line on the rim of the distributor casting. That is Number 1. With the engine at top dead center and the cam lobes for Cyl. no. 1 pointing up, the rotor should point toward that line.

Thanks for the info. I found the line on the distributor rim and the car would not start at all. The car previously ran with a setting with the distrubutor cap rotated 180 degree (to fit the two clips). Is it possible that the distributor was rotated so much (during timing) so that the rotor is as much as 180 degree off the rim line at top dead center?

Joe Alexander: Maybe you should explain how you got to this point so we can help. The mark on the distributor rim is correct position for #1. Now you are either not getting spark or someone had previously changed the correct positioning of the plug wires and position of number one. If so spark plug number one could be on any of the six locations!

This is not the "proper" way of aligning the plug wires as that requires aligning the distributor marks and can involve removing the oil pump drive to get it all aligned properly and that is a little involved to get into here but if you do the following it will get you up and running.

  1. Remove the number 1 (front) spark plug.
  2. Stick your finger in the spark plug hole while you turn the engine over clockwise with a wrench on the crankshaft pulley, when you feel air pressure against you finger this means that #1 cylinder is beginning it's compression stroke look at the crankshaft marking and align the "0" mark with the pointer on the front of the block.
  3. Remove the distributor cap and whichever post that the distributor rotor is pointing at is the number 1. If you lack tools to turn the engine over you can align the timing marks and set up the plug wires using the post that the rotor is pointing to.
  4. Try to start the engine. If it doesn't run, remove the wires and start over with the distributor post directly opposite of the one you used before(180 degrees). You might also want to verify the direction of rotation of the rotor by removing the distributor cap and cranking the engine noting which direction the distributor rotor turns(clockwise or counter clockwise).

Question: How does the oil pump drive indicate ignition or engine timing? Is there a timing mark on the oil pump drive? Does this mean that when removing the oil pump, one has to pay attention to engine timing marks (similar to the Fuel Injection Pump?). Thanks for helping me understand this.

I recently took off the shims below the air compensator on the fuel injection pump because the car was running rich. After a few hundred miles, I check the plugs and found out that #3 and #4 are more black than the others. So I decided to check the firing order. I will try to describe the wire setting.

If the front direction is 12 oclock and the rear direction is 6 oclock, the line on the distributor rim is at 12 oclock and the advance dashpot is at 3 oclock direction. On the cap, #1 plug wire plugs into 6 oclock, #5 into 8 oclock, #3 into 10 oclock, #6 into 12 oclock, #2 into 2 oclock, and #4 into 4 oclock.

The car ran pretty well, running 70 mph at 4500 rpm. I suspect that my distributor is rotated 180 degrees; or that the previous mechanic lined up the disctibutor rim line with #1 with the exhaust top-dead-center. Question: can I find the top-dead-center and rotate the distributor to line up the rim line with the rotor direction?

I don't remember if the distributor has a gear or a slotted fitting on the bottom. SO in answer to your question the oil pump drive has nothing to do with timing the ignition.

Thanks for clearing this up for me. Ny distributor has a smooth shaft with an end that has two male slots on the bottom. I assume those male slots fit into corresponding female slots within the engine. It does sound like your distributor is 180 degrees off the correct position. I am not sure if this is due to incorrect rotation or if it was installed 180 degrees off. Said differently, if the distributor is installed correctly, I am not sure that it could rotate 180 degrees. If installed in reverse, it would easily be 180 degrees off.

Bernt Damm: It's not really that critical as long as the leads match the distributor position. The distributor can't be installed incorrectly because the slots in its underside are off-centre. However, if the the gearing is out too, it can. Put the engine onto TDC with No. 1 cylinder both valves closed (cams up).

If properly installed, the distributor rotor should point at around 2 'o clock if you stand in front of the car. That should be No.1 lead. It moves clockwise 153624. If the rotor isn't there or close, then the distributor was installed incorrecly. Leave it if it worked before and see where the rotor is. Make the corresponding lead on the cap No. 1 and follow with the rest clockwise.

Dan Caron: The distributor DOES go in only one way, but it CAN be installed 180 degrees out. It won't fit well but it WILL go in that way. The slotted connector can also be installed 180 degrees out on the bottom of the distributor which is why I ALWAYS mark them before disassembly.

You can easily move the gear drive after removal of the distributor by using a screw driver and turning it forward and then letting it slide back into place. Moving the wires around the cap will get you by, but you will not be able to use a timing light as number 1 will be in a different place on the crankshaft.

Joe Alexander: when the distributor was installed at the factory, the number one spark plug wire was above the slash mark on the distributor rim. I am looking at a factory photograph of a M130 engine in the BBB (page#00-1/10). With the front of the engine being 12 oclock the condensor on the distributor should be at the 9 oclock position. The number one spark plug and distributor slash mark are almost directly above the condensor.

If the set-up on your car deviates radically from this, then somone at sometime altered the set-up. Of course the car will run fine as long as the plug wires are re-positioned and the car is timed correctly. However adjusting the timing and removal of the condensor may be a problem depending on where the distributor happens to have ended up. Besides it is just not correct.

To re-orient the distributor correctly; Set #1 piston at top dead center on the compression stroke. (For a quick check, remove oil filler cap and make sure the cam lobes on the first cylinder are pointing upward 10 o'clock and 2 o'clock).

Next remove the distributor cap and view the position of the rotor. It should be pointing toward number one spark plug wire and the slash mark on the distributor rim. If it is radically off the mark, remove the distributor by loosening the 5mm allen bolt holding the distributor in place. A small spring should be below the distributor (this is often left out accidentally during repairs).

The nine tooth worm gear below has a slightly offset slot which engages the distributor. A large flat screwdriver can be used to turn this gear clockwise. It will rise then fall back into a different position (as Dan mentioned). Each tooth equals 40 degrees of change clockwise in orientation. Move the gear until it orients the distributor correctly.

Pay close attention that the slight off-set of the distributor prongs match the offset slot of the timing gear or the distributor will not seat down properly. Be sure not to leave out the spring and don't forget to tighten the distributor lockdown bolt when finished. That little spring will push the distributor upward and dis-engage it, if the bolt is left loose.

Pushing downward on the distributor slightly after setting the timing and while tightening the 5mm lock down bolt will keep the distributor down and in place. When you are finished, the distributor will be oriented correctly and the #1 spark plug wire will be in the correct location. An precise ignition timing adjustment with a timing light is necessary to complete the job.

Question: If the engine is running and the plug fires and the timing light is connected to the number 1 plug wire won't the timing mark be in the correct position regardless of which post on the distributor is the "number 1" post(after all the crank is approaching TDC on the number 1 cylinder when the #1 plug fires)? I don't understand how the timing mark could be in the wrong place?

I may be missing that spring as I have not seen it during my distributor work and my distributor has no spring tension when the 5mm allen screw is loose. What is the effect of not having that spring?

If you look in your owner's parts booklet find the table with the distributor, the timing gear and distributor are on this page. It is shown just above the vertical worm gear. You probably would not notice the spring unless you looked down the opening. Your spring may be there.

Normally the spring sits on top of the gear unless removed. It is fairly small and it does not exert that much upward force to be easily noticed. I suspect that its purpose is to restrict any up and down movement of the timing gear caused by load on the gear train during acceleration and de-acceleration.

Any gear movements may cause very small fluctuations in the distributor timing. I do not think it is critical. The fluctuation would be so very small. However you may want to have one on hand for a more convienent time since you just had the timing set.

Dan Caron: That's a good question. You set the distributor to number 1 on the distributor housing and this corresponds directly to TDC on the crankshaft. If you have to move the spark plug wire to any other spot, the distributor is not in time with the engine. It will still work and run but the timing light will strobe at a different spot on the front pulley. Everything HAS to be lined up or your timing light will be of little use to you.

Now I am convinced that my distributor is mis-seated. Before I started to change it I have a few other questions. You stated "The number one spark plug and distributor slash mark are almost directly above the condensor". I found the slash mark is about 120 degree from the condensor on my distributor.

Since these two are hard fixed features, their relative positions should have nothing to do with the distributor orientation. In doing timing, one would disconnect the vacumm line to the advance and block the vacumm supply side. Lined up timing at -30 degree before TDC at 3000 rpm. Is this correct?

I found it hard to find the TDC from the top of the car becuase it is impossible to put a wrench to the crankshaft center bolt from the top. Any tips? What is the plug gap?

Joe Alexander: The distributor rim mark (#1 spark plug wire), was roughly in the 9 o'clock position (plus or minus) when the car left the factory. View figure 00-9/2 in the BBB. page 00-9/2. Some replacement distributors do have the condensors oriented in a different location on the distributor. What is your distributor number?

When setting the timing as mentioned in a previous post, the dwell or ignition point gap should be adjusted first. Now if you have had the distributor out or have done some major repairs and the car is not running you will have to make a rough adjustment before using a timing light. I do a static timing adjustment with a voltmeter or any 12 volt test light.

  • Rotate the engine up close to TDC (top dead center compression stroke #1 cylinder). Be careful not to be 180 degrees off. Remove the oil filler cap and view camshaft lobes of #1 cylinder are pointing upward, (10 oclock and 2 oclock roughly), this indicates that you are on the compression stroke.
  • Rotate the crankshaft to the static timing specification also refered to as "installation value" (10 degree bTDC).
  • Turn the ignition on and rotate the distributor counterclockwise until the voltmeter or testlight just goes out (points open).
  • Snug up the distributor. Make sure the rotor is pointing to that mark on the distributor rim. This should be close enough to start the car and finish the adjustments with a timing light.

Be sure to use the proper specifications for your engine. The manuals show different specs depending on year of manufacture, destination (USA) and high and low compression engines. In your case Vindell, a 1970-1971 manufacture 280-SL (USA version) would be 25-30 degrees BTDC at 3,000 rpms WITH vacuum attached. These figures are out of my 1972 Mercedes technical data booklet p.217. These tables should also be in the BBB as long as it is the latest version(page 00-0/3).

  • Disconnect the test lamp or voltmeter.
  • Hook up the timing light and start the car for timing adjustment.
  • Rotate the distributor until timing meets specs and tighten it up, slightly pushing downward to seat the distributor. New points can settle in and may need re-adjusted after some running.

Don't forget to lubricate the distributor cam with a slight bit of grease. Also, I use a 32mm 1/2" drive socket (1 1/16" will also work) on the front crankshaft bolt to turn the engine. A small 2" or 3" extension and 1/2' drive rachet handle can be snaked up into place from below. A wrench on the power steering pump nut will often times allow slight adjustments from above.

Always turn the engine in its normal direction of rotation. What ever you do don't forget to remove these tools before cranking the engine!
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