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1975 450SL
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Discussion Starter · #1 ·
This post was originally going to be an account, complete with photos, of what modifications I had to make to the Pertonix 1885 kit to get it to fit in the 1975 distributor. But sadly it has turned into a plea for help.

So, I modified the mounting plate to miss the dist plate ground wire and clear the point adjustment nubs, and filed down the advance/retard arm, and got the sensor and magnet installed.

I wired it up to the new "Flamethrower" coil and got.....nothing.

After reading a ton of posts here and on peach parts I concluded that it might be a weak distributor ground, so I added a ground wire as several posters had suggested. No luck.

There was some talk about the gap between the sensor and the magnet, so I filed down the mount to allow adjustment to close the gap. Nada.

I carefully re-checked the wiring:
- red pertronix wire to coil +
- black pertronix wire to coil -
- red/black wire from ignition switch to coil +
- Ground wire from dist points plate to chassis ground
- red/violet wire from starter taped off.
- all the other wiring related to the switchgear, resistors, etc remains in place.

I've got power to the coil and sensor, the sensor has a good ground, and the switched black wire is connected to the - coil post. The bench test procedure for the sensor indicates that it is functioning correctly. I had to drive to work today so I put the points back in and it fired up immediately.

The Retro Rockets website says that most of the sensors that are sent back as "defective" check out ok and the fault is in the car's wiring.

So, before I join these ranks, I'd love to hear from you guys. Have I missed something stupid? The wiring seems embarrassingly straight forward, and I feel like I checked everything. Bad coil? Bad karma? Let me know what you think.

Thanks.
 

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Discussion Starter · #2 ·
One more thing, when I crank the engine I get no spark (inductive timing light) but after cranking, when I turn the ignition off, it jumps once as if turning off the power causes the sensor to switch, discharging the coil?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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This post was originally going to be an account, complete with photos, of what modifications I had to make to the Pertonix 1885 kit to get it to fit in the 1975 distributor. But sadly it has turned into a plea for help.

So, I modified the mounting plate to miss the dist plate ground wire and clear the point adjustment nubs, and filed down the advance/retard arm, and got the sensor and magnet installed.

I wired it up to the new "Flamethrower" coil and got.....nothing.

After reading a ton of posts here and on peach parts I concluded that it might be a weak distributor ground, so I added a ground wire as several posters had suggested. No luck.

There was some talk about the gap between the sensor and the magnet, so I filed down the mount to allow adjustment to close the gap. Nada.

I carefully re-checked the wiring:
  • red pertronix wire to coil +
  • black pertronix wire to coil -
  • red/black wire from ignition switch to coil +
  • Ground wire from dist points plate to chassis ground
  • red/violet wire from starter taped off.
  • all the other wiring related to the switchgear, resistors, etc remains in place.

I've got power to the coil and sensor, the sensor has a good ground, and the switched black wire is connected to the - coil post. The bench test procedure for the sensor indicates that it is functioning correctly. I had to drive to work today so I put the points back in and it fired up immediately.

The Retro Rockets website says that most of the sensors that are sent back as "defective" check out ok and the fault is in the car's wiring.

So, before I join these ranks, I'd love to hear from you guys. Have I missed something stupid? The wiring seems embarrassingly straight forward, and I feel like I checked everything. Bad coil? Bad karma? Let me know what you think.

Thanks.
ADDED in 2021! : Pertronix now say to use the model 1887LS on the 74 and 75 models.

One thing you could do, is first try connecting the Pertronix just as a points replacement using the switchgear & original coil. That is how I have my car connected and the Flamethrower is still in it's box! (Now installed! Car 'seems' to run better!)

To do this, you need a switched 12v supply to the Pert red wire (ign switch side of 0.4ohm resistor) and the black wire runs to same place original points green wire ran. (see pic below)

Doing this would prove that the installation in the distributor is good. Is it possible that with the Pert in place, that the rotor or cap does not locate properly?

The diagram from Peach that I was going to use if I installed the Flamethrower is below. Sounds like you have it connected that way? The wire from the starter is likely not needed - I think that was to boost voltage by by-passing the 0.4ohm resistor during start, was it not?
 

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Discussion Starter · #4 · (Edited)
MBGraham, thanks for your response, I have read several of your previous threads on this topic. I'm assuming that you are also Graham at Peach Parts?

One thing you could do, is first try connecting the Pertronix just as a points replacement using the switchgear & original coil.
I tried this per the photo you posted here, but I was a little bit confused about the green wire. On my car ('75) the green wire goes to a co-axial plug on the switchgear, not directly to the terminal block like it sounds like it does on your car. The set-up as depicted in the photo didn't work, and I also tried it with the black wire connected to the green wire from the switchgear, which directly replaces the points, no luck.

The diagram from Peach that I was going to use if I installed the Flamethrower is below. Sounds like you have it connected that way?
Exactly, the only difference is, rather than using the bypass wire to the resistor, I connected the wire from the ignition switch, and the red pertronix wire, directly to the coil + terminal.

The wire from the starter is likely not needed - I think that was to boost voltage by by-passing the 0.4ohm resistor during start, was it not?
That's my understanding too.

Maybe RadioTek will weigh in here. From what I read he is running a Crane in his '75 but he might have some thoughts on the wiring for this year. Plus it sounds like he's an EE in real life.

Thanks.
 

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I ordered the 1885 PerTronix for my 72, will it also need extensive modification? I am following this very carefully, as I will be doing this in the next few weeks
 

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both of dads 72s had/have the pertronixs hooked up without the switchgear installed, like in the drawing graham posted.

red pertronix wire to the same power that goes to the hot side of the coil.(we simply grabbed 12V on the one side of the resistor)


and the black pertronix wire to the neg. side of the coil(along with the tach signal *I THINK* is on the neg. side)

easy peasy.

the only modification we had to do was lengthen the pertronix wires(we did have an issue cause we simply crimped the wires, and mointure got in there, used some liquid electrical tape, and no more issues)

and install a resistor in the tach line, cause (i believe) the coil was a different resistance and made the tach read high
 

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I ordered the 1885 PerTronix for my 72, will it also need extensive modification? I am following this very carefully, as I will be doing this in the next few weeks
For a start if you have just bought the 1885 without Flamethrower, just connect it as in my picture above. And, add a ground wire from the distributor casing to a good ground (I went straight to battery).

If you have bought the Flamethrower too, still connect as above and when that is working, re-connect as per the drawing above. You may then have to go and buy the resistor at RS to make the tach work. But then, I don't think you have one, do you, so forget that!
 

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I tried this per the photo you posted here, but I was a little bit confused about the green wire. On my car ('75) the green wire goes to a co-axial plug on the switchgear, not directly to the terminal block like it sounds like it does on your car. The set-up as depicted in the photo didn't work, and I also tried it with the black wire connected to the green wire from the switchgear, which directly replaces the points, no luck.
I see in the manual that the 75 has slightly different wiring. But connecting black pert wire to center conductor of wire to switchgear should work. It looks like there should be a test port (TD) from the switchgear. If you spin engine, and check voltage, you would expect to see a 3 or 12v pulse there.

It sounds like the problem is at the distributor. No accidental ground from the black wire or lack of ground from the pickup coil to distributor? or broken internal ground wire between plates?

Maybe a picture might help?

You may have seen these posts about clearances and grounds within the distributor, but they may help:

PeachParts Mercedes ShopForum - View Single Post - Pertronix & Tachometer Query - New member with 1973 450sl

PeachParts Mercedes ShopForum - View Single Post - I took my ballast resistors out...
 

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add a ground wire from the distributor casing to a good ground (I went straight to battery).
so run a wire from where the green wire was to the battery ground in addition to connecting the pertronix?
 

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Discussion Starter · #11 ·
You may have seen these posts about clearances and grounds within the distributor, but they may help:
I did have the issue with the magnet hitting the Pertronix baseplate as well as the vacuum advance arm. I filed away at the base, and the advance arm until it seated all the way down. You can see the notch in the vacuum arm in the picture.

I re-soldered the internal ground wire, as it was a little frayed, but check out the brown wire in the picture, it goes right to the base of the Pertronix sensor so the ground shouldn't be a problem! Rather than the battery, I ran this wire to the chassis ground at the coil mounting bracket, it's the same place that the Switchgear is grounded.

Proctologist: I think that most of the modifications pertain to the '75 model year, as the distributor is a little bit different, utilizing both vacuum advance and retard. Also, the little nubs you use to adjust the points get in the way, as does the ground wire between the plates. I will upload all my pictures to this thread at some point, I am still hoping to be able to say it works when I do!

Thanks all, for your input.
 

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so run a wire from where the green wire was to the battery ground in addition to connecting the pertronix?
No - attach it anywhere on the outside of the metal casing of the distributor - there are a few screws that can be used. The black Pertronix wire is equivalent to the old green points wire and runs to the same location.
 

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I did have the issue with the magnet hitting the Pertronix baseplate as well as the vacuum advance arm. I filed away at the base, and the advance arm until it seated all the way down. You can see the notch in the vacuum arm in the picture.
It looks OK. Only thing I can see wrong is that the rotor is missing ;)

Is it possible that the magnet somehow prevents the rotor from being aligned with the contacts in the cap?

Otherwise, it should work ??
 

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No - attach it anywhere on the outside of the metal casing of the distributor - there are a few screws that can be used. The black Pertronix wire is equivalent to the old green points wire and runs to the same location.
Right, I got that, black wire to ground where green wire went

but then you wrote:

And, add a ground wire from the distributor casing to a good ground (I went straight to battery).

so now I am hopelessly confused, attach black to ground then add a wire from the distributor casing to the battery, the dist casing ground would be where the green wire -was- too, what am I missing? Am I being obtuse? (wouldn't be a first)
 

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Right, I got that, black wire to ground where green wire went

but then you wrote:

And, add a ground wire from the distributor casing to a good ground (I went straight to battery).

so now I am hopelessly confused, attach black to ground then add a wire from the distributor casing to the battery, the dist casing ground would be where the green wire -was- too, what am I missing? Am I being obtuse? (wouldn't be a first)
I am confused too!

Pert has a black and a red wire. Red to 12v as per pic I posted. Black to connector near resistors, also in pic I posted It is NOT a ground!

Run another wire (brown is good!) from anywhere on outside or inside of distributor casing/plates to a good ground somewhere I went to battery negative, but the way michncraig is equally good. Normally the distributor just grounds via it's mounting, which is not a very good ground.
 

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Both the Crane/S&S and the Pertronix systems replace the switchgear as well as the points, they just go about it differently. The Crane system uses an optical system to determine the time to send the pulse to the coil, while the Pertronix uses a Hall effect magnetic sensor.

Mercedes/Bosch wanted to decrease the 'wear and tear' on the points and increase their life by using them to only switch a low current and low voltage. This would reduce arc pitting on the contacts of the breaker points, theoretically eliminating it. The only "wear" part would be the rider that followed the lobes on the distributor shaft.

The High voltage/high current switching to the coil would be done by solid-state electronics at the Switchgear. This is the box behind the left headlight that cost around $275.00 for a rebuilt unit. The electronics are able to provide a much cleaner and sharper pulse to the coil than the points alone.

However, time and heat cycles cause the values and characteristics of components to change. This is where the replacement devices come in. They can provide a clean, sharp pulse again, in a much smaller package, due to technology advances. They can move the switchgear box inside the distributor, in just slightly more space than the points. The triggering is done in ways that eliminate the wear point of the rider on the shaft lobes.

Pertronix does this by a magnetic sensor that detects the proximity of magnets in a sleeve attached to the distributor shaft to the body of the sensor. Crane/S&S does this by using an optical sensor that is triggered by a wheel attached to the shaft with windows (holes) in it. 4, 6, or 8 magnets or holes for the like number of cylinders.

What you want to do is to eliminate the existing switchgear from the circuitry. You can do this by disconnecting both connectors at the box. This should leave the green wire with the coaxial connector dangling at both ends. This is the wire from the points to the switchgear. The Crane unit replaces this with a 3 wire cable from the sensor to its' switching box, while Pertronix uses the Black wire from the sensor unit/switching unit.

Ballast resistors are often placed in series with the Positive (+) voltage to the coil (terminal 15) to create voltage and current characteristics that enhance the spark. If these are not in place correctly, there could be damage to the coil, or the circuit might not work properly. Some coils are equipped with internal ballast resistors, Bosch uses external resistors. When undertaking a conversion, check that these are not damaged and have the proper resistance values. One is 6 Ohms, the other 4 Ohms.

Mercedes, among others, switches the negative(-) side of the coil (terminal 1).

Now that I've tried to explain how this system works, let's try to figure out why yours doesn't.

I note that you talk about 3 wires from the Pertronix unit. The online info on them only mentions 2. Is this a seperate wire, or has another been added somewhere along the line?

I know that you need to have the existing switchgear completely out of the way, electrically. It needs to be completely disconnected and removed, but we can leave that for later when we get the new stuff working.

I have a strong suspicion that you may need to have at least one of the ballast resistors in the circuit to get this to work. When you disconnect the large connector to the existing switchgear, it should go back to a terminal where you have a Red+Yellow wire, a Red+Black wire, and a Red+Violet wire connected together. This may be at one end of one of the ballast resistors.

I would suggest that you tie the Red wire from the Pertronix in there. The Black wire from the Pertronix should go to terminal 1 of the coil (negative term). There should be a Black wire from terminal 15 of the coil (positive side) to a ballast resistor.

Check that wherever you tie down the Red wire from the Pertronix, it has voltage when the ignition switch is in both RUN and START positions.

I seem to remember that you said that you have a seperate Ground lead from the Distributor to the engine/frame. If this is not true, you might want to install one.

Make sure that the magnet sleeve for the distributor shaft is installed correctly. Is there the right amount of distance between it and the sensor? Is it positioned correctly: do the magnets correspond to the lobes of the dizzy shaft?

Did you remember to put the rotor back in the distributor before putting the cap on? (don't ask:eek:)

There have been reports of problems getting the cap back on correctly. Make sure the notch in the cap fits the tang on the distributor correctly. Maybe the magnet sleeve is preventing the cap from seating properly.

This thing should be dead easy to install, if you follow the directions, but I've been in technical electronics for so long that there are things that are so ingrained in me that I don't even think about them, I may be overlooking something.



To get the Tachometer working, you have to get the proper signal to it. The Bosch switchgear had a seperate line just for the tach. This is because the tach is designed to work on a 3 volt pulsed DC signal. The only thing you have now is a 12 volt pulsed DC signal, so you need to bring that down to where the tach will not overload. This can usually be done with a resistor.

The procedure I used when I got mine to work finally was to go th Radio Shack and get a 10 KOhm potentiometer. I connected the middle post of the pot to the Negative side of the coil, and one of the other posts to the terminal shown in the first photograp in post #3, the top center. There is a lug there that is supposed to be where a service tech can tap into the tach signal.

I used a long piece of 2 conductor wire so that I could have the pot in the cabin with me while I started the car and varied the throttle. After starting the engine, I varied the throttle and adjusted the pot until I had the tach working even with the headlights on. Then I shut down the engine, disconnected the pot, and measured the value where I had the best function of the tach. In my case, that was about 6 KOhms.

I then dug around in my spare parts bins until I found a resistor with close value, and made up a lead from the Negative side of the coil, through the resistor, to that terminal strip mentioned above. I insulated the exposed conductors with heat-shrink tubing and now have a working tach.


Hope this helps. Try anything above you want, and report results. Then we can go on.
Scott


I will edit this when I get home, and can include drawings and schematics for clarity.
 

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seems like a lot of work to eliminate a part that only needs a very infrequent simple adjustment and has a useful lifespan of years and thousands of miles.

I can understand your point of view. The thing you may not know about is that there are some 'complications' that can make the job worthwhile.

I had to do mine because I have 'wobble' in my distributor shaft that was eating the rider on the points such that they required adjustment about every two weeks.

Another reason is that the Bosch switchgear can fail or work poorly. When I bought a Remanufactured unit, it was $289.00 plus shipping. The Crane unit was $107.00. The Pertronix unit is $89.00.

Sometimes, it's just like coming into the middle of a movie: There are important things you don't know. :)

Scott
 

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Discussion Starter · #20 ·
RadioTek, thanks for your comments.

I note that you talk about 3 wires from the Pertronix unit. The online info on them only mentions 2. Is this a seperate wire, or has another been added somewhere along the line?
Red & black from the sensor, Brown is a ground mounted to the base of the sensor (see photo in my previous post.)

I have a strong suspicion that you may need to have at least one of the ballast resistors in the circuit to get this to work. When you disconnect the large connector to the existing switchgear, it should go back to a terminal where you have a Red+Yellow wire, a Red+Black wire, and a Red+Violet wire connected together. This may be at one end of one of the ballast resistors.
I'm using the "Flamethrower Coil" (1.5 Ohm) which is looking for a full 12 Volts, and eliminates the need for the ballast resistors.

Check that wherever you tie down the Red wire from the Pertronix, it has voltage when the ignition switch is in both RUN and START positions.
I even tried powering the coil and Pertronix unit directly from the power lug to be sure.

Did you remember to put the rotor back in the distributor before putting the cap on? (don't ask)
LOL. Yeah, I made sure the dizzy was well sorted. Anyway it doesn't matter if the rotor is in there or not, because the unit isn't discharging the coil.

This thing should be dead easy to install, if you follow the directions,
Exactly. That's why I needed a sanity check from you guys before I send back the "defective" part, but I am feeling like I've done my due diligence here and it must be something with the unit itself. I mean it really is dead simple.

Now one more thing I could try just for fun is pull the Crane Ignition that I have in my old Volvo 122 and see if I can get that to work. I remember that the kit came with the chopper wheel for 6 and 8 cyl as well and I think I know where I stuck them....

Thanks again for weighing in.
 
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