All, I scored an 87 diesel wagon in exceptional physical condition but with a bad "14" head, then scored a donor sedan with a replacement 22 head and 100K less miles.

Been driving the wagon with the swapped in motor for a couple of weeks. After a few tweaks, it has been running great, starting at the touch of the key when warm, and with a little glow when cold, no problems whatsoever.

Then, this AM, I turned the key after giving it a good glow...

NOTHING. No sound, click, weak groan spin, nothing. Dash lights are on, all seems normal but no motor spin.

Thought, well the battery had been weak and something drained it. I did not have much time or tools, checked with my Fluke, only 11.9V from the battery. I got a Lyft ride to the office (its close) where I have other cars. Drove the W210 back home, put a charger on the W124 battery.

Later this afternoon my smart charger indicated 100%. Still nothing. Swapped batteries, and again, nothing.

I guess there is a starter solenoid somewhere, my best guess at this moment unless there is a relay somewhere that could be the culprit. Could be the key switch, also, I suppose.

Would appreciate ideas and a link to a wiring diagram for this model (1987 300TDT OM603) Thanks!