W123 OM617 - Not turning

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1985 W123 300TD
Morning All,

So I’m getting on with trying to sort out the ‘85 300TD. It will not turn over. Ignition on, glow plugs actuate, nothing else aside from the click when you turn the key to position 2.

He told me that he’d also been trying to remove and aftermarket car alarm (80s style) and had basically got the hump with it - I’m not sure if this is a red herring with regard to my issue, but I need to ascertain that the wiring is ok (I have an old-school electrician coming this aft).

The chap I got it from had the gearbox rebuilt during his ownership, but the car had not been started since. I’ve performed some simple checks like connections and oil level (a little low), as I thought it could be the Neutral Safety device. I tried wiggling the gearstick and turning key, nothing. I don’t want to disconnect the main plug on he nearside of the gearbox yet as I’m waiting for advice after this post…

There is also a single wire that runs and plugs in to the offside (UK drivers side) rear of the gearbox but I don’t know what that is and can’t find on any diagrams - pictured - anyone?

I saw on YouTube a guy who bypassed the Neutral Safety as a ‘get out of jail’ event by having the ignition on and touching a wire from the terminal block in the engine bay to the positive terminal - but I don’t appear to have the same wires going to it. Could this be my problem, as there’s obviously something non-standard happening at my terminal block (red cable and relay?). Link here:
. I’m wondering if the last chap hasn’t connected everything back as it should be.

Any advice appreciated, pictures attached… thanks all…

Dot
 

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optimusprime

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Wow - First the auto box ATF fluid [oil ] should only be checked properly with the engine running at full operating temperature so it could be over filled now .
 
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Member
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Norwich/London
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1985 W123 300TD
Wow - First the auto box ATF fluid [oil ] should only be checked properly with the engine running at full operating temperature so it could be over filled now .
Not sure that’s a wow moment but anyway 🙂 - atf is showing low and have not touched it yet…

In other news found the neutral safety on the gearbox to be defective - bypassed it and she started.
 
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1985 W123 300TD
So an update with this, with some progress, but still need some assistance please.

I’ve removed the neutral safety / reverse light switch with a view to replace it, but I’m unsure if it was refitted correctly when the transmission was refitted.

In the photos originally, you can see the read with and relay - this is a fuel heater, which I’ve not seen before.

With the switch removed the gearshift linkage appears to click through the gears fine, but I can’t see clearly how the neutral safety connected to the linkage. Along with this when looking for the part 123 540 1945 searching comes up with all kinds of items for later Mercs - is this something I should be going to Mercedes for as a genuine part replacement?

When I got the engine started with the bypass in place, I could not engage any gears when shifting through them all. I got a change on tone, but no movement of the vehicle. I called the guy i bought it from who in turn gave me the number of the company who rebuilt the box, and when I told him the level was about 5mm under the min on the dipstick (engine had run) he suggested that the low oil level could be the reason for that. That’ll be done Tuesday when I get to the vehicle again, bit I’m more concerned about replacing the neutral safety, so if anyone could advise I’d be grateful.

Thanks,

Mike
 

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Thanks Grober, I think I have a vacuum problem somewhere as I’m having to shut off manually, so that could be it….
 

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