Here is what is happening:

Sometimes, I try to turn the key and it is like frozen, won't turn, unless I jiggle/play with it to the point where the glow plug light goes on, then I turn to start the engine, and nothing happens.

OR

I turn the key (like normal) till the glow plug light goes out, turn again, but nothing happens.

What I have been doing the last few times is disconnect one side of the battery, then reattach it again.

Then it will work (glow plug light goes off, I turn the key and it's cranking).

What should I be looking at here? Just trying to narrow down the part that needs to be replaced - any hints would be appreciated.

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1991 300E 124.030 103.983KE 722358 03 412178
207K

1979 240D 123.123 250K (Project car)

2000 Ford Ranger, 187K

2015 Dodge Ram 1500 EcoDiesel 37K

There's a junction box on the right inner fender in front of the battery. Pull up the lid and jump terminals 1 and 3 when the ignition switch is not causing the starter to turn. If the starter turns when jumping the terminals, it's a very strong indication that the problem lies in the ignition switch itself (although it could possibly be in the wiring somewhere).

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Problem started up again yesterday, when I accidently tried to start the car when it was in first gear. Lunged forward, then stopped, but my usual trick of disconnecting the battery for a few moments did not work this time. Tried it 3 times.

Glow plug went on, but then no cranking sound when turning the key further to the right. Then, I remembered I had an original key in my glove box (doesn't work on the doors however, I just saved it just in case). Used that original key and it worked.

Why don't my other (copy) keys work? It's like it's not making contact to start the engine.

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1991 300E 124.030 103.983KE 722358 03 412178
207K

1979 240D 123.123 250K (Project car)

2000 Ford Ranger, 187K

2015 Dodge Ram 1500 EcoDiesel 37K

Take out the ignition tumbler and start the beast using a flat head screw driver. If that works, you need a new ignition tumbler.

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Toblin

'79 300D, "Liesel von Diesel", 235K

I kid proofed the house....but they still get in