123 ignition

[chumps]

I know there are dozens of posts about the 123 ignition and I believe I have read them all. I could not find a problem quite like mine. I received my 123 last week and attempted to install it today. I have a 1971 280SL with everything stock in the engine compartment including the emission control equipment which works perfectly. The distributor looks like it might have been replaced in the late 90's. It has a number ending in 010. I have gone step by step according to the instructions that came with the unit. I have a new coil (bosch red - 1.6 ohms) Everything went smoothly right to the point were it said a green light was to come on in one the holes in the aluminium disk on the top on the distributor.  I turned on the ignition no green light! I bypassed the two resistors by removing them and connected the wires. I disconnected the green wire from the distributor at the ignition module under the battery so it came out with old distributor. The wire that ran from the coil down to the .06 resistor has 12 volts with ignition on. And continues to have 12 volts when fastened to the coil. The problem is when I fasten the red wire from the 123 to the coil (+ connection post) where the original hot wire  is connected as per the diagram in the instruction booklet the voltage drops to near zero. With no electrical current to the 123 the green light can't come on. When I run a hot lead from the battery to the red wire on the 123 I get the green light they are talking about. I have tried everything I can think of - grounding, checking connections, etc. Any suggestions would be appreciated. It appears that I am doing something wrong somewhere. Thanks for the help, Chumps

[WRe]

Hi,
do you still have your transistorized ignition in place?  (www.sl113.org/wiki/Electrical/TransistorIgnition)
I would assume that it will not work together with the 123 ignition.
...WRe

[kampala]

Chumps,

Just confirming the obvious --- make sure your black wire from the 123 unit to the coil is disconnected when you are testing for the green light.  The black wire only gets connected after you have the green light.   Make sure you have nothing at all connected to the negative coil terminal when testing for the green light, and after testing for the green light, only the black wire from 123 unit gets connected to negative coil terminal.

[chumps]

Yes the transistor ignition is still in place. I thought that jumping the resistors and removing the green wire that goes from it to the distributor (no place to connect it to the 123) would over ride the transistor ignition. I followed the  instructions per the booklet. The black wire from the 123 is not connected to the coil yet and the ground wire from the - post is removed. If I connect the wire from the key that goes to the ignition module straight to the coil + it would totally bypass the module and probably work (I think), but nothing says anything about doing that. I hate to start experimenting for fear that I well damage something. According to the booklet, I'v done everything right. Any other suggestions? Chumps

[awolff280sl]

When I installed my 123 I couldn't get the green light to come on either.
To get it working I wired it up, had someone crank the engine, then I slowly rotated the 123 until the engine caught. I remember having to re-orient the drive gear to get the 123 to sit where I wanted it.
Hope this helps.

[chumps]

Thanks Andy. I'll give it a try this afternoon.. Chumps

[chumps]

Is the ignition module interfaced at all with the emissions control equipment on a 1971 SL? By completely bypassing the module will that effect the emissions equipment?  Thanks, Chumps

[kampala]

Chumps,

I can't advise on the emissions as I bypassed them by adapting my throttle body to match a Euro version so the vacuum can be connected directly from throttle body to the 123 as would be done on a Euro model.  

However, I wanted to advise you on how the 123 is wired on my 1971 USA model, in case it helps.

The wire from the ignition key switch is connected directly to the coil positive. It does not go to the transistorized ignition nor does it go through the resistor --- it goes directly to the coil.  Some would argue that the red coil requires a 1.8 resistor, but if you read the fine print, it only requires this if you are not using an electronic ignition.  I may be risking the coil by not having the resistor but for me, the 123 worked better wiring it directly.  

In addition, since mine is a late 280 car, it had the additional wire running from the starter and going to the transistorized ignition.  I have again wired this directly to the positive coil by-passing the transistorized ignition. This wire was essential to having the car start easily.  Without this wire from the starter connected to the coil,  the car would start, but took a lot of cranking.  With it connected, the car starts right away.  

So, to recap, my coil positive has three wires on it -- one from ignition key switch, one from the starter and one from the 123.   The coil negative only has the black wire from the 123. All other wires from transistorized ignition are disconnected.  

See the attached wiring diagram from the tech manual as it shows the original wiring for a transistorized ignition and will help explain what I have described.

Best of luck,

[chumps]

Thank you Kampala for the information. I will try that wiring tomorrow and see what happens. Chumps

[Sept]

I found this thread today.  I'm in the middle of installing a 123 distributor as the old Bosch shaft had some play in it and I'm getting misfire/backfire especially going uphills.  I also had problems getting a green light on the 123 but could get one going direct to positive pole on the battery with the red wire from the 123. Chumps did  you get your unit to work with the instuctions provided here?  My next step is to remove the transistorized ignition unit under the battery. This is a 1971 car built in December 1970..engine is an SE..I'm assuming a dealer replacement as I don't have documentation otherwise.

[Benz Dr.]

I'm not sure I understand why anyone would replace the late ignition system with the 123 unit if the original one was still working OK. What am I missing?

[Cees Klumper]

Poster says his original distributor had play in the shaft, so it wasn't ok anymore. Then replacing with a 123 makes sense, plus it's a superior design / technology over the original.

[Benz Dr.]

Only because it's fully electronic. Loose shafts can be repaired without too much difficulty.

[teahead]

Anyone else having issues w/the movement of the distributor to get the green light in sync?


The instructions say a green light will come on w/the key.

They say to turn the body until it turns off.  However, when this happened, the green light was on, but hidden by the "ring of six oval holes".  So do I turn it until it's off by mere covering the light w/the ring?  Or really turn it off? 

At any rate, it didn't turn off until I moved the ring/rotor shaft as well.  Then it says to turn it the opposite direction until it's back on and the rotor is in position to #1 spark plug boot (on the cap; motor is pretty close to TDC).

I can't get the light to turn on (have to move the body AND the rotor/ring thing) AND have the rotor EXACTLY at the #1 spark plug boot position.  As soon as I have the rotor at exactly at #1 spark plug position, the light turns off.  It's probably like 1/4" from the boot position w/the light on.  Good enough?  Go ahead and start it?

[teahead]

Never mind.  Stupid me didn't have the dizzy all the way in.

 

[Heftos]

Chumps, did you sort out your issue with the 123?

[chumps]

Yes I did get everything working perfectly. I am extremely happy with the 123. Car runs great at any RPM, idles smoothly in gear at about 650 RPM.

[Heftos]

That’s great to hear. What was the problem you had with not getting a green LED during installation? How did you fix it?