dpbrowne,

There are a couple of potential places where you are losing contact. One would be the connections to the starter itself. If you are not getting a "clicking" noise when you move the key to the "start" position, I would start the investigation assuming the solenoid is not getting power.

A week or so ago I went through a troubleshooting exercise assuming power was not getting to the glow plugs on someone's car, and sent them on a search and destroy mission that was probably unnecessary. Apparently the glow plug relay died, so addressing sending power to the relay was not necessary. This time I would recommend you confirm power is getting to the solenoid first.

When you look at the front end of the starter you will see a couple of wires connected to the starter. I am describing this purely by memory as I am not at home at the moment, so you may have to interpolate my descriptions with the reality of what you see looking under the hood. The one on the smaller, outboard body bulge is the connection to the solenoid. It should have a little rubber boot that covers the connector after it is made, but the wire itself has a purple stripe on it I think. It is a smaller wire. The thick one is the connection from the battery to the starter motor.

The solenoid is a linear displacement type device that engages the pinion gear on the starter with the ring gear on the flywheel, and, once it is fully extended and the gears engaged, it becomes a relay to energize the starter. When you let go of the key, the power to the solenoid stops and a spring pushes the pinion gear shaft back into the starter body bulge (sometimes a separate, smaller body bolted on to the starter body). With a low battery charge, or not enough travel, you get the clicking noise as the linear motion out and back is cycled by the key switch. If you are not getting the clicking the chances are you are not getting power to the solenoid.

You can check this by having someone try to start the car while you hold the probes of a multi-meter on the screw holding the wire to the solenoid and the engine block. You should set the meter to Volts, in the zero to 20 Volt range or so, and look for 12 Volts. If you have no Voltage with the key turned to "start" you need to check the power circuit to the solenoid. I am not at home and cannot remember this circuit exactly, but I believe the power comes from the battery to the light switch and from there to the starter key and from there to the solenoid. It is not uncommon for the key's electrical connectors to fail, and I have heard of a few light switches failing. These connections are accessible from under the dash.

If you are getting power to the solenoid and it is not snapping into the start position, you need a new solenoid as a minimum. I would get a new starter from Fastlane, and get the heavy duty one.

There are past posts with very detailed instructions on how to get to the key switch and change the electrical switch out that is connected to the back.

Given your other electrical stuff works, I think the light switch is an unlikely culprit as, I recall the power to the fuse box comes from the same connector on the light switch.

Good luck and I hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)