A 240D Jeep project - your work will not be the onl thing that is slow! Sorry, not an old diesel fan!
Don't let the wiring scare you off - there isn't very much to it. But certainly more than just wiring up a coil or something. I have never done wiring before, but did my own wiring for my 450SE motor with K-Jet, which is the same FI system as a series 1 W126 that I presume your 500 is.
Have a look through a mates photo's that he took - he has done 2 conversions now - Mercmad63 (on here occasionally).
A quick summary of things that need to be done off the top of my head:
- trans tunnel relief around the flex disc (see the pics). Also need a mount for the shifter. Can just merge in parts of the 500 tunnel
- mix and match the finny and 500 prop shaft (I can't recall having to change its length other than mixing different era parts)
- adapt the throttle mechanism to work with the 500 - use a W108 unit and see how the 500 pivots off the firewall - copy the way it works. So some cutting and welding there.
- handbrake on RHD cars is hard to keep standard - don't know about LHD cars though
- you will want a bigger radiator. GGR on here used one from a W112 with the M189 motor. I am getting a custom one made out of alloy. However, mercmad used a finny one and a W126 one with modifications and they worked ok.
- fit the W126 fuel pumps/accumulator/filter instead of the finny unit.
- unlike my 450, mercmad foudn the deeper sump of the 500 fouled on the finny drag link. So he looked at a W108, and noticed it had the idler mounted much lower - so he cut one off a W108 and mounted it on the finny in the same spot - see the photo's
- I remote mounted the battery in the boot to make more room in the bay
- use W108 3.5 or 4.5 engine mount arms
- you will need to solve exhaust clearance issues around the steering box - mercmad and I went the custom header route, whereas I think GGR raised his engine in the bay about an inch by machining about 1cm or so (from memory?) off the engine mounts and put spacers under the engine arms (or mounts) so the manifolds could clear the stering box. He used the R107 tri-Y 5.0 euro headers
- trans crossmember - use one from a W108, it will bolt in
- rear end - you won't want the finny one in there as it will be screaming on the highway - it should be 4.1 wheras the 500 is probably 2.32 or 2.47 or so. Minimum solution is to get a rear from a W108 3.5/4.5, but the best solution would be a 6.3 diff ($$). If you get one of those, do the extra fabrication and fit the anti-lift roll bar to reduce the twitchyness under brakes.
- and the wiring. The K-Jet has minimal wiring. I too will be starting on my coupe soon so I can get detailed instructions from mercmad and from my own K-Jet wiring diagrams and pass them on if required. But honestly, I would't stress about it. I have recently been contemplating fitting a S55 AMG from a 2001 car and yes, the wiring and computers are pretty much a deal breaker (or a wallet breaker!). But not so with the K-Jet.
Finish your other project and start collecting some bits - the engine mounts, diff, and $. But know that you will not get stranded with a project that dies because of lack of help - there are quite a few of us that have done this.
Search for the thread on W111-108-113 mods for some interestign reading.
Drew in Oz
LATE EDIT - just remembered that with a 500, the speedo are electronic. So you will need to talk to an instrument shop about changing an electric signal into a mechanical twist to drive your fintail speedo. I was going to use aftermarket gauges so I have not looked into it.