OM603 into W108 - the electrics

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Dweezil
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OM603 into W108 - the electrics

Post by Dweezil » Tue 27 Mar, 2018 1:06 pm

Hi Team,

trick question for the day...

I'm trying to put an OM603 from a W124 300D into a W108, keeping the 108 instrument cluster. (Yeah, I know, crazy).

What are the minimum electrics/electronics that I'll need, and how much of the W124 wiring loom will I need to keep? Do I need to bring the fuse box as well, or can I bypass that with something inline?

I need to think about:

Temp sensor
Oil pressure sensor
Speedo
Glow plugs (I'll use manual button system)
???

I also know nothing about the computer system. What's the minimum that it needs to function?

In anticipation, huge thanks.

Dweezil

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AMG
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Re: OM603 into W108 - the electrics

Post by AMG » Tue 27 Mar, 2018 4:37 pm

ignition switch - vacuum stop fuel cutoff,
temp sensors should be fine, use existing sensors - probably have the same threads... if not use the new 603's sensors, measure the resistance at room temp and in boiling water - if both are within range of each other then you should be okay. VDO sensors haven't changed much.

speedo should be cable driven if the 722.3 is from a 124. I'm guessing you'll need a custom length cable. The diff ratio is the important thing - the speedo is driven off the output shaft, the speedometer is geared to match the differential. in a 722.3 I'm pretty sure the final drive is 1:1 and the "overdrive" efficiency is occurring in the differential ratio. (3.07:1??? or maybe taller? 2.8's 2.7's?)

If it's 4sp manual then speedo is same deal - cable driven. the only issue is when the speedo drive from your existing trans has a different output to the new trans. i.e. if the final drive is a different ratio. iirc, shouldn't be an issue on the 4 sp auto. Manual 4 sp I think is OK, but it's something you'll need to check.

Glow plug relay is super efficient. use it, and your key will love you.

IP is mechanical. no issues there.

you may have a fuel pre-heater depending on the engines origin. useful in alpine areas where alpine diesel is pricier.

Throttle cable,
vacuum pump (you'll need a decent reservoir I guess)

Is it a turbo engine? you'll want a boost gauge.
Tach signal is sourced from crank angle sensor - diesel and petrol ones are different number of teeth iirc.
no need for ABS or klima relay, because your 108 isn't running the later HVAC. but it would make an excellent retrofit.

Can't think of anything else off the top of my head right now. Is this for Gustav?

Someone else with a more detailed 108 knowledge will almost certainly pickup somethign I have missed.

cheers,
Joe
Current:
1987 560SL 4sp. auto Signalrot "Stella"
1987 190E 2.3-16 5sp. man. Blauschwarz "Hermann"
1992 300CE-24 6sp. man. Perlblau / Iceblau "Gretel"
1992 Range Rover Classic 4sp auto Ardennes Green "Oswald"
2012 E63 AMG Speedshift MCT Diamantweiß "Klaus"
Previous:
1986 560SEL Anthracitgrau "Schultz" - In Mercedes Heaven
1987 190E 2.6 4sp. auto Signalrot "Sabine" - which now resides/owns Andrew M's Garage
1972 350SLC Astralsilber "Lurch" - now in the loving care of Craig B
1989 2.5-16 Blauschwarz 4sp. auto (parted) formerly owned by Derek/Hasan.
2012 Renault Sport Megane RS265 Trophy 8:08 6 sp. man. Liquid Yellow "Jean Rédélé"

Dweezil
C 111
Posts: 925
Joined: Thu 05 Jul, 2007 12:34 am
Model you own: w123
Location: Lovely downtown Katoomba

Re: OM603 into W108 - the electrics

Post by Dweezil » Wed 28 Mar, 2018 1:02 am

Thanks for your fulsome reply, Joe.

This is for Karl-Heinz, Gustav's 6-inch longer brother. Keeping the 124 trans.

To be honest, electrics scare me and electronics petrify me. The 124 wiring looks like a labyrinth and I have no idea what's supposed to go where.

I'm biting off more than I can chew, and I'm trying to chew like mad...

Dweezil

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AMG
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Re: OM603 into W108 - the electrics

Post by AMG » Wed 28 Mar, 2018 8:01 am

Are you around over the next few weeks? drop me a PM, I'll see if I can go for a drive up the mountain, stop by and have a good look at the wiring for you.
Current:
1987 560SL 4sp. auto Signalrot "Stella"
1987 190E 2.3-16 5sp. man. Blauschwarz "Hermann"
1992 300CE-24 6sp. man. Perlblau / Iceblau "Gretel"
1992 Range Rover Classic 4sp auto Ardennes Green "Oswald"
2012 E63 AMG Speedshift MCT Diamantweiß "Klaus"
Previous:
1986 560SEL Anthracitgrau "Schultz" - In Mercedes Heaven
1987 190E 2.6 4sp. auto Signalrot "Sabine" - which now resides/owns Andrew M's Garage
1972 350SLC Astralsilber "Lurch" - now in the loving care of Craig B
1989 2.5-16 Blauschwarz 4sp. auto (parted) formerly owned by Derek/Hasan.
2012 Renault Sport Megane RS265 Trophy 8:08 6 sp. man. Liquid Yellow "Jean Rédélé"

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