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

   

So, if it works all the time when you apply power directly to the starter harness, then I would suspect the starter is okay and the problem is somewhere between the positive battery terminal in the trunk and the junction box up front. All I can think of would be the ignition switch or the anti-theft device.

I did replace an ignition switch on my old 400E about 16 years ago. If I recall correctly, it wasn't that difficult, but it also wasn't necessary--I just ordered the ignition and tumbler all in one order.

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

This post is interesting:

Partial Electrical Failure

Have you checked all the fuses?

MORE QUESTIONS: Have you tried to start the car with the key while in neutral instead of park? Did you notice any other electrical irregularities like lights or accessories not working or any smell of melting plastic? Is the one click that you hear actually the starter solenoid or could it be some other relay under the hood that you are hearing?

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

It's for sure the solenoid clicking.

No other irregularities at all

The nss must be ok because putting it in gear or drive gives no crank no click, but in P or N it will crank, or click@ solenoid.

It has been working intermittently since I jumped it.
I'd say about 70% of the time it will start normal.
If it doesn't, I jump it, it will then remember how to start normally...

It's really weird!

I was thinking it could be the lower harness, but it doesn't make sense that jumping it would work if the harness was the problem. .
Unless I'm missing something?

The wires that go bad on the lower harness are for the oil pressure and quantity gauges. I have never heard of the large starter wire in that harness going bad.

Have you tried hooking up a charger to the battery to supplement it during starts, just to rule out a situation where there is current but it just isn't quite enough to turn the starter?

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

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