Ignition Questions

[Dave]

1967 230 with the black coil.  Read the tech manual, and still wondering

Looking to understand............. I see
A condenser on the outside of the distributor. 
A ceramic resistor on the fender (ballast resistor?)
Another condenser-looking thing mounted next to the coil. 

Ok so,
The condenser on the outside of the distirbutior abosorbs electicity so no arcing across the points.
The ceramic resistor lets all power go to the points during "start", but not during "on".
Is this correct? and then lastliy, the condenser next to the coil, which is attached to the + side of the coil and the ceramic resitor, what does it do?

How do I check to see if everyting is working correctly, voltmeter maybe?  What should I test for?
Thank you

[ja17]

Hello Dave,

The condensor at the coil is for the radio. It filters out some ignition noise.  The 230 SL does not have the by pass feature for the ignition during starting. It is there to cut down the amount of current across the points to keep pitting at a minimum. The 230SL originally had a Bosch tan top coil.  Just find out what coil you have and make sure you have the ballast resistor which is correct for that coil  Use Bosch ignition points. Most other brands do not seem to last. Ikor brand vented points worked good for me also. Test all your ignition wires with an ohm meter to make sure that your wire ends and plug wires are good. Use non-resistor spark plug.

[Dave]

Thanks Joe.  I think I'm beginning to understand.  So the ballast resistor is on the circuit to diminish the voltage to the points all the time?  I have the tan top coil that just died.  I bet it's original.  How do I confirm the ballast resistor rating?  It's pretty ancient, too.  I read on the tech manual that I need at .9ohm ballast resistor. 
Sounds like next steps is to get the correct coil (I used a generic 12v pep boys coil to get 'er running), and a new set of Bosch points and condensor, and a new ballast resistor.  How do I check if the ballast resistor is still good?  Now sure how to check for ohms of resistance.   

I spent the whole summer with a dead car up on jack stands, going after fuel problems, red rusty gas - tank, fuel lines, etc etc then no spark, so it's a joy to do these last few things to square it away and drive!  Appreciate the help.

[mdsalemi]

Dave,

Typically the ballast resistors are either .6 or .4 ohms.  You measure this with the ohmmeter part of any voltmeter--even the cheap $10 ones from Harbor Freight, Sears, or any auto parts store.

Since this resistance is quite low, it is hard to measure completely accurately with a cheap meter.  That's the bad news.  The good news is, if it is "dead" it has infinite resistance, due to the wire being broken.  That's easy to check and measure.  If you have any continuity, it is probably OK.  Problems with ballast resistors often start with cracked ceramic.

They are commonly available from all the suppliers, either Bosch or Beru manufacture.

[georgem]

Hi Michael,

Just to pick up on the ballast resistor; does the wire do the resisting and how is the ceramic involved - my resistor has been broken in two for several years and I figured as long as the wire was good and the ceramic stayed in position it would cope, which it has, but now you`ve got me thinking that I should replace it.

Cheers

George

[twistedtree]

The ceramic is just to dissipate the heat.  It's generating 5-10 watts if my math is correct, which will make it pretty hot.

[ja17]

The ballast resistor will be matched to the particular coil used. So the original ballast resistor may or may not be correct for any non-original coil. The coil manufacturer most likely will indicate the ballast resistance to be used. The engine will run great for a short time with no ballast resistor at all. However the ignition points will pit badly and burn prematurely without it. Yes, the tan top Bosch coil was most likely the original for your 230SL.

[Dave]

Thanks Joe.  I think the right thing to do is get the red Bosch non-transitior coil and a matching ballast resistor, a new set of points and condenser, and off I go.
Really appreciate your help, and all the other folks who helped me wrap my head around this.

[jacovdw]

...Typically the ballast resistors are either .6 or .4 ohms...

Michael,

The values you quoted are applicable to the 280SL's with the transistorized ignition setup.

For the 230SL using the original black coil the ballast resistor would be 0.9 Ohms and would have a gold plated metal bracket (Bosch).
If you are using the current replacement coil (Bosch red coil) then the required ballast resistor will be 1.8 Ohms (red plated metal bracket).

[Dave]

Thanks Jaco
How nice of you to reply all the way from RSA.  You described my car.  Now I know it was the original coil and ballast resistor.  45 years of service, not bad!

Here at my local car show in suburban Chicago USA there is usually a beautiful new Superformance roadster on a regular basis.  I enjoy teasing my friends having them guess the continent and the country where it came from.  They never get it right!  It is easily the fastest car there. 
Cheers and thank you for the information!
Dave

[jacovdw]

Glad I could help Dave... 

[georgem]

One last question before this thread finishes:

I have checked the SLS site and they list numerous coils and ballast resistors - how do I identify  the correct coil for my car - later 230 and the matching ballast resistor?

cheers

[ja17]

Hello George,

You will need the std, coil for a standard ignition (with no factory electronic ignition). The original coil was a tan top. The new replacement will be correct for your ignition  but a different later version.

[Benz Dr.]

The main thing to understand is that all the parts of your ignition system need to be matched to each other. Plugs, wires, distributor, coil , ballast resistor and throttle body. Get one of these things wrong and the engine probably won't run well.

[Dave]

New Bosch red coil (came with the bracket!) and matching red ballast resistor.  Jackpot!  Never ran so well.
Thanks to all for the help.