W124 – Installing on-board Trip Computer

Greetings to everybody who is reading this!

I have been collecting the information about trip computer for three years already and finally I am ready to share it with you: I have all the required information as well as time and wish to do this. I am assembling the trip computer on Mercedes W124 with the M103 engine.

The trip computer elements include the dash panel, the remote control, the control unit, and the wires. I will start my story from making the wires. I take this wiring scheme as a basis (click to enlarge):

I have edited this scheme slightly to make it easier to understand, and added the color specifications.

Here is the control unit itself (marked N41 on the scheme above).

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One friend of mine told me that I am going to have problems with assembling, as there are no places you can buy such connectors nowadays, but I would like to say that there is a solution to this issue. After inspecting the device I found out that the N41 connectors are quite similar to the ABS ones – the difference is minimal.

Here is the connector:

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And here is the difference:

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Touch a piece up with a file to make it fit:

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Also we need to tuck the holding lock as the original version has a different angle of wires outlet.

Disassemble this connector: use a drill tool to take out the old wires and the old filling. I found no filling among the older 1989 year wires.

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Take out the contacts themselves to set them to proper positions later and to make the soldering more comfortable.

I had several wire sets from W124 and W201 models and found all the colors needed except the following:
I changed yellow/blue to yellow/dark blue
blue to dark blue
gray/pink to gray/purple
blue/white to dark blue/white
blue/brown to blue/red
black/purple/yellow to black/purple

I suppose that such changes will not cause any questions in the future even if you did not know about them.

We assemble it in the reverse sequence.

I would like to point your attention to the fact that you need not to forget to remove the white holding locks on the edges of the connector; otherwise you will be unable to take out the contacts.

Insert the contacts according to the numbers specified on the scheme (on the connector itself they are specified on the reverse side).

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It is better to purchase the whole set of wires for W124 with M103 engine as we will need a couple of more contacts in the future that can be taken from the KE control unit connector, as well as certain other connectors needed (we will get back to them later).

I had to adapt the control unit connector, as it was too large. The control unit did not fit to its slot due to the connector.

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Now let us make a round connector.

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In order to do this we take a standard 15-contact dash panel connector and adapt the dowel with a file.

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There are the contacts numbers on the inner side.

Now let us move on to the most difficult connector. We need to make a plug for this connector:

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I had to spoil a number of connectors in order to understand that the ceiling light one fits best.

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It has two sectors: the first one with two contacts we cut off and put into waste, and the second part we are going to need.

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Now let us make a cut in order for the holder lock to have something to catch on.

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Counter-drill the inner holder of the contacts (pins) for them to get deeper, looking out of there.

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As we are doing a plug we also need to make an orientation pin. Take the fat contact for this purpose, however you will need to shorten it, but you will cope with it when being inside of the process.

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I have removed the numbers that were specified on the pad: we are doing a plug out of a socket, so, basically, they should be going in the reverse direction. Not to make a mistake use the correct order that is specified on the dashboard pad.

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Here is what I have got.

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What I forgot to mention is that you can also use the contacts (pins) from the ashtray: there are three of them so you will need two ashtrays correspondingly. Also such pins are present in the PTF E500 wires, inside the seat heating system, electric curtains, and lambda probe.

The remote control pad. The similar one from the outer lights control. Without any changes, all the contacts are signed with corresponding numbers.

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I attached the brown wires near the W1 link. The X83 pad is under the oven. The X6/1 is next to the hand-brake cable. The X35 is next to the battery pack.

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F1 “11” and “6” is the fuse block, so 11 and 6 are the fuses.
X21/2 – the electronic speedometer pad – is attached to the Hall sensor.
I attached X29/3 to the diagnosis pad (next to the battery pack), but using the tray next to the fuses.

X61 is the trip computer pad that is being connected to the N3 block (the KE control unit), namely to the contact #4. Sometimes the harness may lack this very contact but it is not a problem to withdraw it.

All other wires, contacts and connectors specified on the scheme are present in the basic wire set.

Here is the result:

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Everything works fine; I drive my car and feel fully satisfied. Good luck to everyone!

Provided by wolf wagner

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2 Responses

  1. johan says:

    where do u get the led screan to display l per 100 km used

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