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Discussion Starter #1
I have been searching for a month or so for a write up or explanation from anyone who has retrofitted a trip computer into a w126 but have come up almost empty. One member from a Mercedes site in the UK says that he has done it and was very easy, just a couple of wires to hook up and you are done, but did not mention what wires to where.

I have also pulled up the diagram in the electrical section of the wis for pre-1986 w126's and have everything figured out with exception of the white with blue stripe power wire that goes to the fuse box. My question is, which fuse number does the white wire with blue stripe go to (this wire is in the main harness for the back of the cluster from the fuse box)? Or for that matter a complete breakdown of the diagram color codes to fuse #'s. I suck at reading electrical diagrams.

I would be grateful for any help with where the wire goes or even better a point towards a write up on this project by another member.

I have the full harness as well as the cluster (speedo in true MPH). I would like to do this when I once again swap out my dash for a color change. Makes it very easy to work the harness out with the dash out by the way.

One last request is the translation of the instructions from German to English. Sadly, all the previous posts of the translations have expired.
 

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Computer Instruction Manual

Greg,

Here is a copy of the instructions for the dash computer.

You owe Dr. Grills for these, he found them in a wrecking yard.

The wiring some times has a number ident on them if not attach a copy of the wiring and I will take a look.
 

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Discussion Starter #3
Beautiful Jon! Spoke with the good Doc about this. I will try and post the diagram again. Seemed to be too large but will screen shot it and see if that works.

I was able to keep the fuse # identifier on one of the wires when removing from the car but had to cut the white/blue at the bulkhead and there are two similar wire colors in attached under the box.

I will post back this afternoon when I get home. Thanks for the file you posted.
 

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Greg, if you need my help, LMK. I'm looking through my stuff for a schematic. It should not be that hard to wire in though. I'll PM you if I find it. As you may recall, I dallied with the thought of installing one in my car.
 

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Greg, if you need my help, LMK. I'm looking through my stuff for a schematic. It should not be that hard to wire in though. I'll PM you if I find it. As you may recall, I dallied with the thought of installing one in my car.
Thanks. Just looking for what # fuse in the panel that the white/blue wire goes to. Got everything else wrapped up last month but can't figure the last wire.
 

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Discussion Starter #7
Thanks for the encouragement oisaj dude! I have thought this to be a fascinating option for years but after trying to figure out which way was up with the wiring harness a couple of years ago when looking at a car in a junk yard I thought it was just too much work. But I pulled the dash from the donor car of this cluster and harness and realized that Mercedes probably just added the harness after the rest of the wiring was in the car but before the dash went on. This extra harness was just cable tied onto the regular harness and the computer brain for it was just up and right of the cluster.

I am not going to install the trip computer until next month or so when I do yet another complete interior swap out. Don't ask. But I will show pictures now of the complete harness and list a small index with each picture of where the wires connect (with exception of the white/blue wire, which I have no idea which fuse it goes to).

Donor car was a 1985 euro 500 SEL with unknown month of the build and it is going into my 84 euro 500 SEC. Every single part of the donor car was GEN I with the exception of the base of the fuel distributor (metal base that the fuel distributor sits on on is held on with the rubber boot on the intake. There was a sensor on the passenger side that one of the plugs from the harness plugs into. More on that later.

I will take pictures when I actually do this project and post them onto this thread but for now, here are pictures of everything you will need.

This picture shows the entire harness, the computer and the instrument cluster:
 

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Discussion Starter #8
This picture is of the only 2 parts of the harness that go into the main engine compartment. The wires come out of the "brain" harness, run along the passenger side under the blower fan and out through the firewall grommet on the passenger side, under the battery tray and through the false firewall. The 3-prong connector labeled "1" connects to the sensor discussed above that is on the side of the piece that the fuel distributor sits on. The eye connector labeled "2" connects to the 3rd position from the front in the little plastic connector box that sits on the frame well on the passenger side (right next to the oil filter housing).
 

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This eye connector labeled "3" is connected with the rest of the existing wires that are screwed onto the "power with lights on" power block that is inside the center console near where the drivers knee would be closest to the drivers side of the console.
 

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This picture shows all the wires that reside behind the cluster. I mistakenly connected the 6-pin rectangle connector for the control switch in the center console to the back of the cluster but the rest is correctly connected at the cluster.
 

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#5 goes to the ground bundle behind the cluster closet to the cluster. I have no idea where #6 plugs into, but I believe I might have taken too much of the previous harness from the donor. It should plug into the green wire somewhere.
 

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Greg, I'd like to bring over my wiring harness to compare to see what needs to be done to get it complete. I had to cut a few cables off and now need to splice some wires to get it complete.
 

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Discussion Starter #16
These last 3 wires go into the main fuse block. From left (the broken wire), grey/black or possibly white/black goes to fuse position #1. In the center is 2 wires that are red/black that go to fuse position #12. The one on the right is my big mystery as to which fuse position that it goes to. It is white/blue and is just a single wire.
 

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Discussion Starter #17
This last couple of pictures shows the back of the cluster with all the wires connected just from the trip computer add ons. The places that have no connectors come from the original harness. Last picture is the plug connector for the center console controller switch.
 

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Discussion Starter #18
Doc, I will bring the harness and the cluster with me when we meet up this coming weekend. Really not to much to it. I will post up the schematic in a few.
 

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Again, I can really only see doing this with the dash removed. Once you remove a dash for your first time, it really only takes a half hour to remove and several hours to get it back in. Good time to do the vacuum pods and put a good clean dash in all at one time.

I will post more when I get the cluster in. If you need any pictures of a specific part I will post it up for you.
 
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