280SL Ignition

[n/a]

The ignition circuitry in my 1968 MB 280SL includes a Bosch component marked with the number 0332 010 001 that includes a relay with one set of normally open contacts.  These contacts are used to bypass the resistor that is in series with the ignition coil and the source of 12 volts from Fuse 2 when the Ignition Switch is in the Start position.  The contacts are connected to terminals 1 and 2 of the components cable connector.  Terminal 4 of this connector receives 12 volts, apparently from a contact in the starter, when the Ignition switch is in the Start position.  I believe that terminal 3 connects to the junction of the coil and the series resistor.  

I have been unable to locate a wiring diagram in various 280SL/8 owners or service manual that describes my particular ignition circuitry that includes the above mentioned Bosch component.  In trying to start the car, after a careless, long period of not being used, I found the engine would not fire, and that the full battery voltage was not being applied to the ignition coil.  It did, when temporarily jumpered dirctly to the battery's positive terminal.  Is the component faulty, or have I made a mistake in rewiring the system?  I am confused beause I have had no similar problems since purchasing my 280SL in 1968.

Can anyone tell me what the Bosch component is called, and how it should function?  

James D. Garls,

jdgarls@ntslink.com


1968 280SL
One owner
Restored and engine rebuilt 1999.

[ja17]

Hello James,
The later 280-SL cars with the higher horsepower starter motors did have a ignition ballast resistor by-pass. One of the two small lugs on the starter solenoid activated this by-pass when the starter was engaged by the ignition switch. If the ballast resistor is bad the car will stop running when you take your jumper off. Verify this by jumping accross the terminals of the ballast resistor itself. The ignition normally operates at a lower voltage, except when starting (later 280-SL with bypass). Ignition points on a stored car can become coated with a tarnish or oxidation which is an very good insulator. This can be very stubborne to remove. Check to see if power is getting to one side of the points but unable to crossover to the otherside. Good luck.


Joe Alexander
Blacklick, Ohio

[n/a]

Mr. Alexander,

Thank you for your helpful reply.  I have carefully studied the ignition system of my 280SL, and agree with you that battery terminal voltage is switched via contacts in the starter to a plug-in relay unit, located near the coil, that contains a set of normally open contacts that by-pass the ballast resistor at startup.  That relay does not operate when 12 volts from the starter is applied to terminal 4 of its cable connector.  Inspection shows that the unit is not a simple relay.  It contains some transistorized circuitry that controls the energization of the actual relay coil.  I am unable to determine whether or not a faulty component in the circuitry prevents the relay from operating.  I am awaiting a reply from Bosch to my request for information about the unit; however, it may not be available since it was made more than 35 years ago.

I have thoroughly inspected and cleaned all of the ignition circuit components, and have installed a new distributor cap and rotor.  In addition, the coil produces a healthy spark when bench-tested with a fully charged battery.  A quick test showed the engine to fire when a jumper from the battery was applied directly to the coil.  This, of course, simulated the action of the relay's by-passing contaccts, and suggested a malfunctlion of the relay unit.

If anyone has a similar setup to mine, and could provide me with a hand drawn sketch of the visible wiring of the coil and ballast resistor, it would give me assurance that I have made all the connections properly.

One final point.  The base and cover of the relay unit in question is insulated from the chassis by rubber mounting grommets, but the base has a connector lug to which an external connection could be made.  Is this connection required, and if so how and where to?

Thanks Joe, and anyone with additional information.

James Garls

1968 280SL
One owner
Restored and engine rebuilt 1999.

[ja17]

Hello James,
Something does not sound quite right here. I have the factory wiring diagram for this circuit somewhere. I will look for it and get back with you. You may be looking at the emission timing relays! There are two of these on the later USA 280-SL's. They are the only relays with internal circuitry.


Joe Alexander
Blacklick, Ohio

[n/a]

Joe,

The factory wiring diagram for my 280SL will be of enormous help in solving my problems.  I pray that you can locate it, and can send a copy to me.  My address is:  824 Henrietta St., Pekin, IL 61554-3445.

Thanks for your help and encouragement!

James Garls

1968 280SL
One owner
Restored and engine rebuilt 1999.

[ja17]

Hello James,
I have located my factory USA 280-SL wiring diagram (thanks Achim.) In addition I have also found my factory wiring diagram for the timing and RPM (USA emission cars). This is not in the BBB but are among some factory supplimental literature I have. I am quite sure these are the relays you mention. Exactly what is the problem you are having?
I will try to scan the info for you Sat.



Joe Alexander
Blacklick, Ohio

[n/a]

Joe,

When trying to start my car after a long idle period, there was no ignition spark.  This was tested from the No. 1 cylinder plug connector to the chassis, and from the ignition coil to chassis.  I do not recall all in the chain of events that led me to test all of the components of the ignition system and the wiringl.  At one point, after removing the coil to prove it was without fault, replacing the distributor cap, rotor and condenser, I carelessly removed the distributor to replace the insulating washers where the lead from the points exit the distributor housing.  This will, of course, create timing problems later, but for now it is not the problem.

To be certain all electrical connections were good,  all terminal were cleaned of corrosion.  After studying the wiring diagram in my owners manual, and diagrams in several other manuals, I learned that most systems applied the full battery voltage to the coil at start up, and that the voltage was lowered by a "ballast" resistor after the engine was running.  A voltmeter test showed that the battery voltage WAS NOT at full battery voltage at start up.  When a jumper was connected from the battery to the coil, the engine fired, so I looked for the way the battery voltage would be applied to the coil.  I discovered the circuits did include a ballast resistor with leads that could connect to contacts that would bypass the resistor.  These leads went to a connector that plugged into a relay....what I thought would be a simple relay.  I found that one of the other of the four leads to the connector received the batttery voltage (appx. 12 volts) when the ignition switch was in the Start position.  This seemed proper to energize the relay.  The fourth lead to the connector came from the ignition coil's primary connection (15).  At this time, the purpose of this lead is a mystery.)

The relay did not operate when the ignition switch was in th Start position!  So, it was concluded that it was defective.  I then removed it from the car, removed its case, and discovered it was more than a simple relay.  I have previously described it to you.  I can not understand why it need be anything more than a simple relay, and I am tempted to delete the transistorized circuitry to make it just that....a simple relay. I am sure the box has no function that is emission control related, but it may be identical to those that are.

As I write, my thoughts return to the mystery lead mentioned obove.  Can my problem be that this lead should connect to the ground side of the coil, which then goes to the ignition points?  A correct wiring diagram could  quickly solve my problem.

I again thank you for all your help.

James D. Garls

1968 280SL
One owner
Restored and engine rebuilt 1999.

[Skitzerow]

Do not know if you solved your dead spark situation.  But make sure you do a check on the screw that comes out of the distribor with the wire that goes to the coil.

This screw needs to be be fully insulation from the distributor body.  Otherwise it grounds out the whole spark system and gives you no spark.  This wire is the one that comes directly from the points.



SDK

[Skitzerow]

Make sure if you have a dead, or no spark on your ignition to check the distributer to make sure the wire from coil to points in distributor is insulated and not ground to car.

Where the wire comes out of the distributor there is an insulator coming through about an 1/4 inch hole.  There is also sometimes an insulator washer inside the wall by the hole that is missing or falls off when you are changing points. If you lose the insulator and the points, or coil wire connects with the distributor housing to be grounded you will not see a spark.



SDK