I did the conversion a few weeks back, here is some information if anybody needs it.
This was for a 1990 Mercedes 1617 NG, OM366 engine. I think alot of Mercedes models from this era were the same in terms of wiring, so may be useful for 1017's and unimogs etc
As it existed before:
Remove trim around sterring column below steering wheel (4 long bolts), this exposes the steering lock mechanism, built into which is also the ignition wiring and ignition barrel.
On the left hand side are 3 wires soldered on.....one red (constant feed), one black (turns ignition electrics on). and a black/yellow wire which runs to 86 on the starter relay to fire the starter motor.
On the right hand side of the mechanism above the ignition barrel is a 2 prong wire plug (both black from memory)......these will cause the steering lock to come on (connect them and disconnect them with the ignition on and you will hear a click in the mechanism, this is firing the steering lock pin).
So, I completely removed the whole mechanism (will have to use a grinder to cut it off unless you have a special tool, the 2 bolts have a peculiar shaped head). Therefore the 2 prong plug is no longer needed as I have removed the steering lock (I dont want it as it could be a real pain to be in the ass end of nowhere and find its jammed on and you've lost or snapped the ignition key!)
I then got an earlier Mercedes NG ignition switch that can be mounted through a hole in the dash. It has a unique shaped key, which is pushed in.....once in, the ignition becomes live. There is no need to turn the key to position 1 or 2 UNLESS you want to wire your headlights onto the additional attachements........but our 1617 has a seperate switch for headlights so there is no need to do this.
So red wire goes to one side of the barrel, black goes to another port which becomnes live when key is pushed in (brings electrics on), then run an additional red wire from the other main port of the ignition barrel to one side of your starter button, then connect the exisiting black/yellow wire to the other side of the starter button to trigger the starter relay when you press the new starter button.
Very primitive and simple, and removes the danger of steering lock coming on when you dont have the key......true, you could just remove the 2 prong plug so the steering lock pin never fires, but the way ive done it now also removes the danger of snapping the ignition key, as with the different ignition switch/barrel I have installed, you dont need to turn the key, just push it in and then push the start button.
Hope some of that helps anybody who wants to do the same.
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