My 1993 400e will not start!

I'm pulling my hair out on this..

Last week, it refused to start. Turning the key produced one click.
I thought the battery might be weak, so I jumped it off my truck, started right up.
Drove it down the road, started back up twice, third start was no go...

Figured it was the battery so replaced that.
Still just one click..

Starter under warranty, so replaced it from Napa with brand new one , not remanufactured, new.

Put it on today.
Click only...same thing, No change..


I've had problems with the immovilizer before, when I did, it wouldn't even click.
So it's not that.


Anyone help point me in the right direction to save my hair?

When you jump start the car (you say that works) are you connecting both cables to the battery, or are you connecting the negative to chassis ground. If the former, I'd check the negative cable from the battery to the chassis for a good ground. If the latter, I would make sure there is good contact between the cables and the battery terminals. Check the voltage across the battery terminals when car is running, then turn the car off and check again. What's the difference between the two readings?

I think Akorna asks some good questions and I would start there too.

If that doesn't work, I would add the lower engine wiring harness to the list of things to check. This harness feeds your starter. When you replaced the starter, did you notice if the harness was deteriorated? Usually, you will see the insulation on the smaller wires of the oil quantity and pressure sensors flake off first.

Also, behind the module box on the passenger side is where the lower wiring harness mounts up. It is under a plastic cover. Check that the connection there is good. Being in Florida, there could be some corrosion at that terminal. You might want to do a search here for replacing the lower wiring harness on a 400E, E420 or 500E and you might get some good pics of where the upper part of the harness mounts.

I am pretty sure there is also at least one grounding terminal behind the right strut. Check for corrosion there.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Jumping it no longer works

I will look at the wiring harness and start at the junction box.
By the starter, the wires look good/new.

Where exactly is the last ground you spoke of?

This car has very little room to work so location of where I'm looking is needed

Thanks!

See attached grounding points and lower wiring harness cover behind module box.

Attached Thumbnails

   

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Ok I went to where the harness plugs in.

Pulled the plug out and gave the big pin direct power.

It fired right up!

Plugged it back in, and it fired up again.
Tried again, and... click..

Unplugging it and giving it direct power jumps it every time.

Is there a problem with the power source to the plug??

Will it jump start every time now if you do it from the battery?

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

The key/ignition/ normal way is 50 / 50.

Jumping it is 100% .

All I'm doing is touching the big pin on the plug to a power source @ junction box 3 inches away

I'm not sure that I'm understanding what you mean by the big pin and junction box.

You might want to try posting your issue over at *********.com to see if those guys have any ideas. The 400E and 500E are virtually identical cars when it comes to electrical issues like yours.

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Ok where the lower harness plugs in is a plug.

Inside that plug are a few pins, the largest one is a direct line to the starter.

As soon as you jump that pin to direct power, the car fires right up.

Pic one is of the plug behind the module box
Pic two is of the plug once undone showing the big pin.

Attached Thumbnails

   

Yup tried the battery jump.
No luck.
Battery is also brand new and retested

I'm wondering if the ignition could be a culprit?

Today tried to start it.
First try click
Second try click
Third try fired up.

Doing nothing but turning the key.

If it's not that, there's a compromise in the power source going to that plug at some point.
Nit sure where tho

Just a couple of other thoughts:

First, have you pulled and cleared all the codes? There could be a code that points to the problem. Intermittent neutral safety switch failures have been known to occur.

Second, ruling out the starter itself being bad, some of the starters on these cars have shims on them. Whether or not the car has shims is dependent on the individual car. Some have none; some have one or two. I don't know if incorrect shimming would cause the solenoid to stick, but it might be something to research.

UPDATE: Also, although the fuses may look good, looks are deceiving. Pull out fuse #8 and check it carefully. If you don't have a replacement fuse, clean up the ends with some fine sandpaper and reinsert.

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

If you replace fuse #8 and it's still not working right, I would pull the instrument cluster and jumper terminals 30 and 87 of the K38 relay. This is the relay that disables the ignition if the anti-theft device under the passenger floorboard is unplugged. This link will show you where the K38 is and how to jumper it. How-to: Disable alarm on a 1993+ W124

Don't worry about unplugging the anti-theft module; just go for the silver ice cube relay (K38) and bypass the starter kill circuitry. The instrument cluster will come out if you can hook a 90 degree pick behind each side and pull it straight out towards you. You might have to extend the telescoping steering wheel to get it out. Mercedes makes a special hook tool for pulling the instrument cluster out (pic), but you can improvise.

Good luck and let us know how it goes.

Attached Thumbnails

 

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Fuse position 8 says its for the tail lights.
Is that the correct one?

Attached Thumbnails

 

Check fuse 5 as well. Need Help...on vacation, car won't start

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles