Had my hands full with a few other old Mercedes. Getting back to the 280se 4.5 (which did run a few years ago). Now, there is no spark coming from the coil to the distributor. Still has the factory points-ignition set-up, so I ordered new points and a condenser. Didn't cost much so no biggie.

My question is, even with a lame condenser, shouldn't the ignition still spark?

Tested coil with volt-meter and it's in the appropriate range - 2.8 to 3.0

I'm just hoping it's not the switchgear, ICU, spark box, or whatever else I've heard it called.

Guess I could have posted this after I installed the new parts, but I'm looking forward to learning how all this ignition units function together.

Thanks for any response!
Todd

On the Mercedes from this era the 'ignition control' can be the cause if the car has been sitting for a long time. The repair is easy, though.

The plugs on this control unit are silver plated so they do not corrode like steel. They do tarnish, and the result is no spark to anything.

Clean all the connections with some electrical contact spray (which you can best get at Radio Shack) and if need be hit them with some silver polish. Just make sure to check them with a continunity tester to make sure they are passing voltage.

Look inside your distributor cap where the wires plug in. If there is any blue powder present clean it up too. This is evidence of arcing, by the way.

Also check the continunity of the wire running from the ignition control to make sure the wire has not broken down inside, and remove your ground wire from the battery and the car and clean both ends of it. It will build up a lot or resistance if it is allowed to sit.

Pooka

Did you try just running some wet/dry sand paper over the points? You can do that, then leave the dist. cap off, take the coil wire out of the center of the cap (carefully) and lay it near something metal. Then turn the ignition "on" and flick the ignition points open with your finger. Each time you flick, you should get a fat spark from the coil wire. If you get a spark, you know you're back in business.

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Didnt think there was a condenser with the standard ignition box setup ?

Most people clip the condenser wire on these. My 4.5 has never had a condenser, but it does run fine. I would not run anything abrasive over the points (sandpaper or silver polish). I've usually used index or business cards.

What I would do is see if the coil is getting voltage at all by connecting a 12v bulb to the 2 coil wires (with the coil not connected to them) and if it flashes, it's a bad coil. That's how I determined it was my ignition box when I was first resurrecting mine some 8+ years ago.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Thanks for responding guys. Will act on all your advice.

Like I said, did test the coil with the volt meter, but didn’t think of testing the end of the wire that plugs into the distributor cap. Smart. Will do that too.

Tomguy: so you mean disconnect the 2 wires from the coil (one from the starter that goes through .4 and .6 resistors and the other from the icu), and with the key in position 2, touch a bulb to each wire end, one at a time? Or do I do this when the car is cranking?

Todd: nice trick. Will try not to shock the crap outta myself!

GaryF: from what I’ve gathered from the web and junkyards, the 280se 4.5 and the 73 and 74 450se have condensers and the green wire. 75 and on just have the green wire. Think it has to do with the retirement of the d-jet system

One more question while I am here. What is the correct route that the power takes?

Starter to .4 resistor to .6 resistor to the + of the coil. Then what? The coil fires and sends power to distributor cap and rotor and then out to each spark plug? And what about the green wire to the ICU?

Sorry. Have some Plymouth guys helping me and they are a little stumped by the ICU. Said it's very "ford"!

While cranking the car you should have a 12V bulb attached to the wires. You should see it flash while cranking. If it does not then the coil is not getting a signal from the ICU.

The ICU is really just a switchbox (think of a transistorized relay) that prolongs the life of your ignition points by sending the low voltage signal to them instead of the 12V that'd otherwise be used to power the coil. If the ignition is left too long in the "Run" position with no cranking and the points are closed, it's sending voltage to the coil the whole time and the box can overheat. It could also blow out the ballast resistors.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

you are right,the US delivered cars have completely different ignition set up to other markets and this has caused a lot of Angst on these forums over the years.

If I'm not mistaken, there are two 12v power wires. One to each of the ballast resistors.

This picture that I made might help... (from http://douging.smugmug.com/gallery/6008570_TbFcX)


I don't want to spread bad info though and I'm certainly no expert. It should help you at least a little but may not give you all of the answers. After taking it apart I'm still confused... This system as installed in my car did not give me power at my coil. I have since switched to a Pertronix and am getting power so the factory harness will stay buried in my garage.

[quoteStarter to .4 resistor to .6 resistor to the + of the coil. Then what? The coil fires and sends power to distributor cap and rotor and then out to each spark plug? And what about the green wire to the ICU?

Sorry. Have some Plymouth guys helping me and they are a little stumped by the ICU. Said it's very "ford"! [/quote]

Which green wire?,there are normally three,a large diameter wire from the distributor to ICB,that is essential because it's the main lead and is a specific length. if it's broken you need a new one,you cannot join it and expect points to last very long. Then there is a small green wire,the previous post shows where it goes and some markets have a green with yellow tracer and that is for the tacho feed.
Keep away from Non mercedes owners when seeking advice...ha ha

If you have power to the resistors on both sides,and the coil is OK ( resistance checks out OK) then the only thing that can be faulty is the ICB,the switch box. Coil failure on old mercedes is common so I would replace that first. The resistors seems to last 40 + years without problems. Have you double checked the points?
Checked the rotor resistance? yes there is a resistance built into the rotor between the tip and the center contract point. Put your meter across it and ensure you have continuity.

Just to clarify because my picture was not as accurate as should be. The green wire in the ballast harness in my picture above goes to a block mounted on the radiator support. Then from there it goes to the condenser on the distributor. I would take this block off but I stripped one of the screw heads...
Pic of the 'block':

Thats not important ,and it won't stop the car running,it's just a very early type of diagnostic point. The old time dealers had a plug that fitted in there so they could check ignition timing.
I really think you should just get another coil and ICB to get your car running.Everything you said so far points to a either or both having failed. it won't hurt to replace the condensor .

thanks again guys for all the info. am gonna put all the ideas to work this weekend when i have some daylight to work on the car. test all the signals, clean metal parts, install new points and condenser and take it from there. there's a junkyard only a few miles away with some 4.5's (i know, sad, but good for me!) so if i have to, i'll pull a few switchgears and coils and see if i strike gold.

will let you know how it goes.

hey douging

was gonna ask you if you could find the part number off of the pertronix ignition. but was in the gallery and saw your pictures of the distributor. 50AB V4. is that the right part number?

might go that if the stock ignition won't come back to life. thanks.

I have the Pertronix Igniter 1 #1885 and the Flame-thrower coil - 1.5ohm, 40,000v, #40011. The number on the Ignitor unit itself must be an internal part number for Pertronix or Vintage Performance (where I bought it from).