Yes, I know I screwed up bad with this one. I listened to someone who thought they knew what they were doing (but don't as I can attest to now) and tried to patch the ground that had broken from the coil to the engine block. (I was ADD and couldn't wait till next week when the ground comes in from Germany)

Long and short is that 1 wire super heated and melted most of its sheathing away. Its the red/cream colored wire that goes from the ignition coil to the fuse box, into a plug then out the other end. I inspected every bit of it and discovered that the wire is the only one w/ exposed copper - which is good. The bad part is that I have no idea where this wire goes to beyond the plug. I saw it route down under the area w/ the other relays and off it went.

So now I need to fix this ASAP as I am afraid of fire. Where does that particular wire go/is there a wiring scheme that anyone has that will tell me (the car still runs fine by the way)? How much work am I looking at to replace the entirety of that harness (I can't even find them online to buy)?

Also, if the car is working fine as it was before, should I be as concerned as I am right now (on a scale of 1 to 10, I'm roughly an 11)?

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87 300E
202k on the clock

Sounds like it may be the 12VDC power from the fuse box through the engine wiring harness connector and then to the Diagnostic socket.
The ground that you broke is probably the ground to the diagnostic socket which is why the power lead over heated.

It should be an isolated power feed used for the diagnostic socket.

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Just to clarify, the ground was from the block to the ignition coil (this is a brand new coil by the by). The actual wire that got really hot went from the 10mm screw on the ignition coil through the wiring harness/sheathed wire to the fuse box and into the plug. On the plug, the pillar that was used is the bottom left most pillar when looking at the plug with the wires coming from the bottom.

Hopefully that helps, and I really hope you are right about the power wire, but I didn't see it go to the diagnostic socket.

Oh and just in case I disconnected the battery for the night - I am afraid of fire.

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87 300E
202k on the clock

You have incorrectly grounded the EZL terminal of the coil, causing a comple circuit of the coil.

The 12v feed to coil is Rd/Pk from the #7 fuse, this is terminal 15 of the coil. [ pos side of coil]
The #1 terminal of the coil goes to the EZL input for switching the ground side. [ neg side of the coil]
The only GROUND on the coil is the case .
Where dd you hook a ground wire on the coil??

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A Dalton

The ground went (and was present on the last coil before it broke) from the 10mm terminal on the coil to the chasis where it met the ground to the block. Previously, the 10mm terminal of the coil was grounded to the block and then it broke off and subsequently I was running w/out the connection to the block. The parts department at my local dealership confirmed that there is supposed to be a ground from the block to the 10mm terminal on the coil (or at least they saw that in the diagram, but they could be wrong as well I guess).

As soon as this happened, I removed what I had done and now I just have this one fried/melted wire, which is red/yellowish in color which is really scary to me.

On a side note, where would I find information regarding replacing the entire wire I screwed up or perhaps the entire harness that was involved? I looked under DIY in the engine electrical and couldn't find anything.

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87 300E
202k on the clock

10MM terminal means nothing to me.
The terminals are Numbered. Which terminal are we talking about. I have your Schematic posted up on a screen right here.
15 is ign feed and 1 is EZL switching.
If there is a ground wire on the coil, it is NOT on a circuit terminal and if you put it on a circuit terminal, that is why you burnt up the feed wire.
The car will still run w/o a coil ground.. the ground is for RF noise.

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A Dalton

When I say 10mm terminal I mean that there are 2 terminals, one on the right (10mm - requires a 10mm socket to remove) and one on the left (8mm - requires an 8mm socket to remove). The two sizes and the right and left correlation are when the post for the ignition wire is at the bottom. I just went out and looked, and there are no labels on either of the terminals. All I know is that one is bigger and one is smaller and the bigger of the two is the one I put the ground on, as well as the one w/ the red/dark yellow - or pinkish wire is fried/melted on.

If you are referencing the plug inside the fuse box, if the wires enter the plug from the bottom, it is the bottom most pillar on the left - I repacked everything in the fuse box to move the car (I was blocking my mother in). I can check this tomorrow when its light out and I can take the whole fuse box apart again if this is what you would like me to look at.

My main concern is whether or not it is safe to operate the car if only one wire is exposed in places.

Finally, thank you for your help thus far.

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87 300E
202k on the clock

The ground wire goes to one of the mounting bolts, not one of the terminals. A ground on either terminal will cause a short circuit and that is why you burnt the ignition to coil feed wire from the fuse box.

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Ignition%20Coil&url=http%3A//img.eautopartscatalog.com/live/F300034900BOS.JPG

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A Dalton

So then just to clarify, this particular wire that I burnt, where does it go and is this particular wire exceedingly important to the running of the car? If the car still runs normal, should I be overly worried about getting this fixed, or is this wire like was mentioned earlier, just a power wire for the diagnostic terminal?

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87 300E
202k on the clock

Just to clarify..

You have burnt up a main ignition feed wire from the fuse box to the coil..
CHANGE IT .

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A Dalton

Thank you for your help so far in clarifying what I actually screwed up. In a previous post you mentioned to have the wiring diagram for this car, so I had one more question - its probably a silly one.

When I do go to change this, it goes through a bundle of wires to the ignition coil which I can't really get through. Would it be acceptable to bypass that harness with the proper gauge wire and send the wire from the coil (which terminal should it go to? I can't expressly tell) to the plug and then crimp it to the wire at the plug? I just don't want to end up doing something when I should have done something else instead. Also, when the wire leaves the plug and heads to the back of the fuse box, where does it end up going to? I just want to make sure I replace everything that needs replacing.

On another note, the car runs better now that it ever had (no more skipping at idle, no more low idle), and all of a sudden lights which didn't work before now work again (like the light in the glove box), so it seems that doing this somehow made the car better, or maybe just shortened its life, who knows.

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87 300E
202k on the clock

You can run the new wire outside and along the harness..just cut the old wire when you get the new wired so that you know no power can go down that line. [ just leave it as a dead line]
I can not tell you how bad or how far back the wires burnt..you have to see to that ..just look.

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A Dalton