Identify Plug Please

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Charlie Buckett
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Identify Plug Please

Post by Charlie Buckett » Sat 28 Oct, 2017 3:02 pm

I am terrible at reading schematics and don't have any for my 1989 m103.
I am bypassing my NSS and Ignition by bridging from the hot side of battery to the middle prong on this plug (as was advised to another member on a really old thread I cannot find anymore).
But what I need to know is if I am bypassing the solenoid as well? or by starting the car in this manner does that mean that the solenoid is functioning correctly? and that it must be the ignition (I have fitted and aligned new NSS already)?
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Christo C
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Re: Identify Plug Please

Post by Christo C » Sat 28 Oct, 2017 6:33 pm

As the wire hasn’t vapourised yet you are not bypassing the Solenoid (the full starting current will vapourise any wire thinner than your little finger ~ about 25sqmm).
On my car that centre pin (thickish 2.5sqmm violet wire) is the solenoid wire. I surmise you are merely bypassing the ignition switch.... and your solenoid is working fine. 😀
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sat 28 Oct, 2017 9:14 pm

Thank you, very happy my solenoid is not the issue.
Am wondering the safest way to connect a push switch to bypass the faulty ignition?

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Christo C
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Re: Identify Plug Please

Post by Christo C » Sat 28 Oct, 2017 10:49 pm

Did you not solve this with another ignition switch (per viewtopic.php?f=6&t=24406) ?
Or be 100% sure it’s not the transmission switch? Have you tried removing the transmission connector and bypassing the switch to confirm ?
What year and model is your W124? (Very useful to add that to your profile or signature)
Thing is, you need to be very careful running additional wiring that is directly connected to the battery as the risk of shorts and fire is very real....
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sat 28 Oct, 2017 11:17 pm

Thanks you for your reply. No I did not replace the ignition switch as I was still uncertain as to whether it was the solenoid, but you appear to have helped me rule this out.
I appreciate your warning as to connecting to the hot side of the battery. (but ignorance confuses me as to why the yellow wire, with an inline fuse, which I presume is the stereo, is connected to the + battery without fire/harm?).
I did mention in this post that my model is 1989 M103 (300te).
I will research bypassing the connector switch (Apologies I have never heard of this).
But still, there must be a way of connecting a push button switch as a cheaper/easier alternative to repairing the 'supposed' faulty ignition? (As JohnAlb rekons he did in post viewtopic.php?t=24053 )

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Christo C
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Re: Identify Plug Please

Post by Christo C » Sun 29 Oct, 2017 7:40 am

(but ignorance confuses me as to why the yellow wire, with an inline fuse, which I presume is the stereo, is connected to the + battery without fire/harm?).[/i]
The clue is in the fuse .... if the wire shorts or draws too much current downline from the fuse, the fuse will hopefully blow before any damage can be done, as long as the correct value fuse has been fitted.

I am somewhat against advising "bodgy" repairs rather than finding and repairing the true culprit, especially as this bypasses what I see as an important safety feature - the Neutral Safety Switch in the transmission, but I suppose you could either

- run a heavy wire to a suitable push-button switch on the dash and back to that connector, as long as you make sure it includes a fuse very close to the Battery end and be very sure there is good insulation / abrasion protection (e.g. rubber grommets) where the wires run through the Firewall and other metal panels. The original wiring uses a wire with copper area 2.5mm² which is quite thick, as even the Solenoid current is quite high - here, starting my car this way an 8A fuse provides sufficient current to power the solenoid.

- or -

- locate the 'correct' wires already installed to the Ignition Switch under the dash and splice the ends to a suitable push-button switch nearby (this assumes your Neutral Safety Switch in the transmission is functioning correctly).

Looking carefully at the wiring diagrams for my car, when the Ignition Switch is moved to the "Start" position additional connections are made simultaneously to the Fuel Pump Relay (pin50) and KE Control Unit (pin16), which is why I think either the second option above or indeed proper repair of the system is ultimately necessary.

[Footnote: I realize the 'factory' starter circuit is not fused, but it is carefully designed and run with suitably heavy wiring and insulation, where all penetrations through panels, junctions and connectors etc. are well protected by rubber grommets and heavy insulation - but it is always worth erring on the side of caution when installing additional wiring as electrical fires near engines are mostly exceedingly unwelcome events.]
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sun 29 Oct, 2017 10:16 am

Christo C wrote:
Sun 29 Oct, 2017 7:40 am


- run a heavy wire to a suitable push-button switch on the dash and back to that connector, as long as you make sure it includes a fuse very close to the Battery end ...
I would only need an inline fuse for the battery wire, or would I include an inline fuse for the connector as well?

- or -
Christo C wrote:
Sun 29 Oct, 2017 7:40 am
locate the 'correct' wires already installed to the Ignition Switch under the dash and splice the ends to a suitable push-button switch nearby (this assumes your Neutral Safety Switch in the transmission is functioning correctly).
I did replace the NSS and tested it with a multimeter, so all should be good, not the solenoid, so only leaves the ignition which I thought I could repair myself but I cannot find any guide on PeachParts or anywhere on the internet for an early w124 M103 (only tumbler removal, no actual switch removal).
Christo C wrote:
Sun 29 Oct, 2017 7:40 am
Looking carefully at the wiring diagrams for my car, when the Ignition Switch is moved to the "Start" position additional connections are made simultaneously to the Fuel Pump Relay (pin50) and KE Control Unit (pin16), which is why I think either the second option above or indeed proper repair of the system is ultimately necessary.
When I disconnect that plug and the ignition is turned to 'on' the Fuel Pump and other relays kick in.
I am considering paying an auto sparky to install this. www.ebay.com.au/itm/Universal-Car-Blue- ... 1438.l2649

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Re: Identify Plug Please

Post by Christo C » Sun 29 Oct, 2017 10:59 am

I would only need an inline fuse for the battery wire, or would I include an inline fuse for the connector as well?
Just one fuse close as possible to the Battery.
My car has 2 other thin wires at that 3-pin connector - I do not know their purpose....
When I disconnect that plug and the ignition is turned to 'on' the Fuel Pump and other relays kick in.
Yes, afik they will still behave as per normal, I am saying there are additional connections made to the Fuel Pump Relay (pin50) and KE Control Unit (pin16) only while the key is turned to "Start" and the Solenoid is activated - I do not know the purpose or reason for those additional connections during the Start phase, but I assume they are of some importance otherwise why are they there....?.

BTW Removing the transmission connector and identifying which pins to jumper in the connector (thereby bypassing the transmission switch) then attempting to Start as normal will tell you:
- if it starts: that the transmission switch is still faulty or in the wrong position.
- if it doesn't start: very likely the Ignition Switch is the culprit (though it could be a broken wire or connection somewhere).
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sun 29 Oct, 2017 3:57 pm

Thank you so much for sharing your knowledge and time, very helpful.
I would like to have it replaced properly but was quoted $700ish for a pro to do it.
And oddly I cannot find a thread on the entire history of the internet that outlines how to do this on a w124.
I tried to do it myself, but having dismantled my instrument panel, lower dash, removed drivers seat... I discovered that the switch is not screwed or bolted to the ignition assembly as was suggested by the seller, but is riveted, I only bought the switch ($68 plus postage) and could not afford the entire assembly complete with barrel/tumbler that I don't need to replace.
I aligned my new neutral safety switch with the allen key guide, and the reverse lights come on, so I am going to trust that the switch is no longer the issue.
I will buy this from ebay www.ebay.com.au/itm/Universal-Car-Blue- ... 1438.l2649 and hope it wont be too costly for an auto electrician to put in (I dont like splicing wires, and may not do it correctly)

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Re: Identify Plug Please

Post by AMG » Wed 01 Nov, 2017 6:48 pm

That "plug" looks like the air pump clutch plug. It's been disconnected obviously, as the connector is hanging in front of it.
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Christo C
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Re: Identify Plug Please

Post by Christo C » Thu 02 Nov, 2017 3:41 pm

Charlie, I was just working on my car so I had a careful look at that plug, socket and wiring.

3 wires:

- 0.75mm² Brown+GreenStripe = Oil Pressure Sender - runs from pressure sender unit just below the Oil Filter to the dash Instrument cluster. When the 3-pin plug is out the Oil Pressure Gauge reads "3" (max) when the Ignition is On, but engine NOT running. Does yours do that?

- 2.5mm² Violet+WhiteStripe = To Starter Solenoid.

- 0.75mm² Brown+BlackStripe = Low Oil Level Switch - runs from switch on side of left sump to the dash Instrument cluster.

Now I observed something interesting.
I started my car as normal with key, with the plug inserted.
When I pull the plug out (with the engine running) the engine idles @ slightly higher revs, and when the plug is mated again the revs settle down as per normal. So I started looking carefully at the circuit which I briefly described in an earlier post....
when the Ignition Switch is moved to the "Start" position additional connections are made simultaneously to the Fuel Pump Relay (pin50) and KE Control Unit (pin16)
i.e. when the Key is turned to 'Start', +12V is momentarily connected to the Starter Solenoid (via the Neutral Safety Switch), the Fuel Pump Relay and the KE Control Unit, or to put it another way, the Neutral Safety Switch, the Fuel Pump Relay and KE Control Unit are permanently connected.

And my conjecture for the observed rise & fall in idle speed is that when the car is in Park or Neutral the Starter Solenoid is connected 'across' the aforementioned connection and is 'seen' as a low-impedance, but when the car is put into Reverse or Drive the Starter Solenoid is NOT connected 'across' the aforementioned connection - I assume this allows the Fuel Pump Relay (which also controls Cold Start Valve) and/or KE Control Unit to 'know' whether the car is Starting or in Park/Neutral or Reverse/Drive and adjust idling etc. appropriately....

So the upshot of all that is that I think the plug does indeed need to be plugged in for "normal" engine operation and gauges, and starting be achieved (assuming that the Ignition Switch is at fault), as we discussed, by either
- replacing Ignition Switch. (maybe too f****ing difficult)
- fitting a momentary bypass 'start' switch across the wires at the Ignition Switch.
- fitting a momentary bypass 'start' switch spliced to supply +12v (via a fuse) to the centre wire (pin) of the connector (as you have been doing, but with the connector also engaged and the additional wire spliced in).
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sun 05 Nov, 2017 10:36 am

Thank heaps for that reply.

My oil gauge worked perfectly, Until (dah dah dah dah) I started my car like this for about the fiftieth time, now it reads 3 ALL of the time, perhaps I accidentally bridged it with + battery.
Also I do not notice any discernible change in revs when the plug is connected or disconnected, but I must admit I am not sure that this may not have been the case in the past.
Seems like I am doing damage, I would love to treat her better but only have casual work at base pay at the moment.
I purchased the switch kit with relay from ebay and it should be here this week. I will attempt to install myself.

The instructions read to connect blue wire to 15(ign) and the red wire to 15 (the power that passes through the ignition).
The starter switch has 15, 15R and 15X,
Could you please identify/confirm which would connect to blue and which would connect to red?
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Re: Identify Plug Please

Post by Christo C » Sun 05 Nov, 2017 12:17 pm

Charlie, I’m away from car and circuits till the 17th or thereabouts .... and only reading this on tiny iPhone screen; but in any case it would be unwise of me to recommend any connections for red and blue wires unless I knew what they are!
Step 6 in the Installarion Description seems confusing to me. Are there two blue wires?
~Christo
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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Sun 05 Nov, 2017 2:02 pm

Wow! Kind of you to reply when you are away and only have a phone screen,
I will happily be patient until the 17th or after, just glad to be getting informed and knowledgeable help.
Yes there are 2 blue wires, from the instructions it doesn't seem to matter which is connected to 50 (starter motor control), only that one blue wire must be connected to 15(ign) and the red to 15 (the power that passes through the ignition).
My car is a 1989 m103 300te, the only schematic I can find is this...for a 1986/88 260E,I don't want to suppose anything and have no experience reading schematics.
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Re: Identify Plug Please

Post by Christo C » Mon 13 Nov, 2017 5:27 pm

OK on my car I would
- splice one BLUE wire to the same wire that also runs to Terminal 50
- splice the other BLUE wire to the same wire that runs to Terminal 15R
- splice the RED wire to the same wire that runs to Terminal 15
- connect the BLACK wire to Chassis / Bodywork / -Ve of Battery

That way the new "Start" button should only work when the key is turned to "ON".

"splice" above means join the wire to existing wire and insulate the junction well; do not disconnect existing wire.

Here the relevant wires are quite thick & colour coded thus
Terminal 50 - 2.5mm² Violet+WhiteStripe
Terminal 15R - 2.5mm² Pink+YellowStripe
Terminal 15 - 2.5mm² Pink+RedStripe
but they may well be different colours in yours....
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Mon 13 Nov, 2017 9:00 pm

Thanks Christo C,
Great timing! The switch kit arrived today (ebay seller said item location Australia with 7 days postage, but was shipped from China and took much longer.)
I will check to see that the wires are the same colours in my model, I'm fairly optimistic as I can't imagine a reason not to keep them uniform across the models.
I am so happy to have received your help.

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Re: Identify Plug Please

Post by Christo C » Tue 14 Nov, 2017 5:11 pm

To tap into the thicker 2.5mm² wires, which are roughly 10AWG, use something like these:
https://www.jaycar.com.au/yellow-quick- ... 6/p/PT4737
which will handle 12-10AWG (2.05mm² - 2.58mm²) diameter copper.

and how to use:
https://www.youtube.com/watch?v=WFdVkSaHRpU
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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Re: Identify Plug Please

Post by Bartman4800 » Wed 15 Nov, 2017 2:13 pm

Christo C wrote:
Tue 14 Nov, 2017 5:11 pm
To tap into the thicker 2.5mm² wires, which are roughly 10AWG, use something like these:
https://www.jaycar.com.au/yellow-quick- ... 6/p/PT4737
which will handle 12-10AWG (2.05mm² - 2.58mm²) diameter copper.

and how to use:
https://www.youtube.com/watch?v=WFdVkSaHRpU
Christo, to be honest I have very bad experiences with these scotch connectors over the years.
Whenever I bought an older car and lights or other appliances were failing, these buggers were the culprits..
They work for a while, and later on they become loose over the source wire.

Here is a far better option if you do not want to solder, and even better if you do apply some solder:

https://www.youtube.com/watch?v=D4b_gSciGIg
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Charlie Buckett
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Re: Identify Plug Please

Post by Charlie Buckett » Wed 15 Nov, 2017 4:48 pm

I am more into tangible mechanics, never been good at electronics/maths etc.
I didn't know about the scotch splicer, and I thank God Christo sent the links or I would have been under that dash, in a footwell, cutting wires in half and using 3 way connectors or squeezing too much gauge into a butt connector. The loom is so short and bundled that I think even if I had dropped the steering wheel any method other than the scotch connectors would have been epic for me. This was so simple, connecting the 3 wires took just minutes, literally, maybe 3 minutes.
I did read comments that these scotch connectors can allow for corrosion, so I used dielectric grease and bound with some electrical tape. So Easy!
I could not have done this without you Christo.

It's not the prettiest looking addition I have made to my beloved Benz (I decided to paint over the words 'engine start' and the brand name 'pivot') but I did save $700 that I didn't have. THANKS Christo.

Switch and Relay $10.99
Connectors - pack of ten $4.55
Time (remove panels, connect with scotch connectors, make hole for button, reassemble) 1 hour.

P.S Don't place a switch where I placed mine (I had no idea the lower dash was made of dense impact foam and sheet metal).
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Christo C
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Re: Identify Plug Please

Post by Christo C » Wed 15 Nov, 2017 5:28 pm

Yes Charlie & Bartman, I am aware of the possible shortcomings of Scotch connectors, but knowing the difficulty of access to wiring in that position they seemed to be a reasonable option to recommend; its almost impossible to get wire strippers in there and the chance to break or reef out a wire there is high. Good idea to grease & insulate as you have, even though the environment inside cabin is relatively clean & dry compared with most other places in a car!
Glad to be of assistance 😎
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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