Well, the parts arrived. I bought a aftermarket Febi ignition tumbler (didn't want to paid $200 for a matched key to VIN one from dealer in Canada) & a Mercedes ignition switch (this was cheap from online).
After some thought, this is the only way I can explain what might be happening.......
With the tumbler out and I use my key to turn the switch, I can start the car every time this way. So therefore I rule out the switch.
Even though the tumbler turns, seems to work just fine. But it has some play (worn), I can wiggle the key left & right without the tumbler being turned at all. With that in mind, I turn the key to start the car..I think the tumbler doesn't turn all the way to have the switch make contact to start the car.
MB has conveniently provided this single pin plug by the firewall near the brake booster for easy access to the starter's solenoid. One end is connected to the solenoid, the other to the fuel pump relay's pin #12.
With the "OLD" tumbler still installed, by turning the key to either "run" or "start"...I get +3.95V.
With "OLD" tumbler out, by turning the switch with the key, in "run" I get +3.95V & in "start" I get +12V.
With "NEW" tumbler installed, by turning the switch with the key, in "run" I get +3.95V & in "start" I get +12V.
As Arthur Dalton elegantly puts it & thanks to his PMs!
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Then the tumbler is not turning the switch all the way to make a good contact for the starter sol circuit.
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