[71w114250]

I hope the kind members and their families of this forum are well.
I've got a 1971 250 with the M130 engine. The "stay at home" has given me time with my car. I've run into a problem and I'm trying to understand the ignition system. It's a points and condenser set up with what looks like the original spec coil. The battery has been replaced with one that allows space for an overflow bottle. Now for my questions. First, there's a very non-Mercedes jumper wire wound around the poles of the white ballast resistor, what's up with that? Second, the low voltage lead to the distributor seems to come from a box sheetmetal screwed vertically under the front of the battery box, is that original to the car? I'll include a picture or two.

 

[Bondjames]

No not original. Not sure what is being done Does it still have points and condenser or retro fitted with electronic ignition?

 

[71w114250]

No not original. Not sure what is being done Does it still have points and condenser or retro fitted with electronic ignition?

Thanks for your reply Bondjames.

My car still has it's original points/condenser set up.

For a little more background, I've had my car since October and have put 6000 miles on it. I'm really enjoying the car.
PPI revealed the car to be in very good mechanical health. There is however an absence of service history.
There's been a couple of bugs in the electrical system. For example, originally there was no power to the brake switch (hence no working brake lights). Performance of the car on start up has been very good except for a failure of fuse 4 causing the cold start (and turn signals) to not work. But having replaced the fuse things are right again.
With some spare time, and a warm garage, I've begun to look closer at the engine compartment's wiring. I have read some of the threads regarding the advantages for switching out the points for an aftermarket electronic ignition. I removed the distributor cap and noticed it was not particularly clean inside so there's some maintenance in my future and maybe a decision to switch out the points for one of the electronic ignition systems.

One of the things I have done is make and replace the ("-") ground wire to the coil. It's length was short and forced the coil HT exit to orient directly at the power steering reservoir. Lengthening the wire let me rotate the coil in its mounting from 9 o'clock to 7 o'clock. The other side of the coil ("+") leads to the ballast resistor. The ballast resistor was not mounted to it's support so I've mounted it on the same bolt as the heater fan ballast resistor but have to ask what's up with the wonky jumper wire on the ignition (coil) ballast resistor?

I'm now wondering if the module I've discovered at the front of the battery box is part of some idea to improve spark while still using the normal points and ignition? The module is hard to get at and see so maybe the next project is to remove the battery box and get a better look.

Do you or anyone in the community have any knowledge for the history of spark improvement tricks and is this possibly one of them?

 

[Mike D]

The original set up used the ballast resistor to reduce the voltage down from the 12-14 volts created by the charging system to a lesser amount to reduce wear on the contact points. The points themselves merely activated the separate transistor box which then provided the signal to the ignition coil. The ballast resistor was bypassed during the starting/cranking phase to allow full voltage by means of a separate feed circuit activated by the turning of the key.

A needless overcomplication of the basic Kettering set-up.

As you will find in your journey of all things Benz, electricity and electronic components are not a strong suit of German engineering.

 

[71w114250]

The original set up used the ballast resistor to reduce the voltage down from the 12-14 volts created by the charging system to a lesser amount to reduce wear on the contact points. The points themselves merely activated the separate transistor box which then provided the signal to the ignition coil. The ballast resistor was bypassed during the starting/cranking phase to allow full voltage by means of a separate feed circuit activated by the turning of the key.

A needless overcomplication of the basic Kettering set-up.

As you will find in your journey of all things Benz, electricity and electronic components are not a strong suit of German engineering.

Thanks, where is the transistor box and what does it look like?

 

[Mike D]

Google is your friend.

Might not look exactly like this but close enough.

 

[71w114250]

Thanks again Mike D.
Sorry I’m unfamiliar. Is it normally mounted under the battery box?

 

[Bondjames]

I went with an electronic ignition retrofit in my 72 450 and loved it, worked fine, performed well, just remember not to leave your key on in the accessory position!