Ignition system trouble

[RadioTek]

My kid told me a few weeks ago that the Benz wouldn't start. He and a friend had hosed it down to clean off accumulated dirt. I finally got to do some diagnostic work yesterday, and it points at the Ignition Control Module. With the key ON, I should get a difference at the 15 terminal of the coil when the points are opened and closed. 12 when open and 2 - 3 v when closed ( or vice versa), I'm getting 12v all the time.

Since I have this problem with the Ignition Module, I was wondering if I could solve it by going to a breakerless ignition setup?

The problem that I have is that Pertronix doesn't seem to have a unit for my application ('75 450SL) and Crane was sold to S&S Cycles and no one seems to have the XR3000 available. I seem to get the idea that there are a few XR700 unit available, but I don't know if that one would work. The 3000 seems to dynamically control the dwell, while the 700 doesn't.

Does anyone have any comments or suggestions? Or am I barking up the wrong tree here?

Thanks,
Scott

[ctaylor738]

My diagram shows that with key on, battery voltage goes through 2 preresistors and then to terminal 15, which means you should be seeing around 3-4 volts there regardless of whether the points are open or closed. So if you are getting 12 there, maybe the preresistors have been bypassed.

[Richard Wooldridge]

Or, maybe the coil is open... or as you said, maybe the ignition control module is defective.
My '82 quit on me last winter and I found the ignition control module was bad, but also after replacing it I found that the coil was the wrong type for the car, and ALSO, the coil to distributor wire was defective, had an open in it that probably caused everything else to fail. There seems to be different coil types for different years, the one in the '82 380SL only works for a few years worth of vehicles. (no resistor on those years). The point being - make sure that you get the correct parts to fix the problem! My '79 has an entirely different coil, and different ignition module, and uses two resistors.