"The wire oxydized because it was in contact with OXYGEN, not heat"

You're setting up a straw man. Nobody claimed that oxygen wasn't involved in the transformation of copper metal to copper oxide. Any chemical reaction, such as the oxidation-reduction reaction that copper wire experiences when it becomes copper oxide and begins to conduct poorly, proceeds much more readily with increasing temperature. Indeed, in this case, the conversion of copper metal to copper oxide is caused by overheating. Anything you can do to prevent overheating will forestall the conversion of the copper metal to copper oxide

"...and the failure mode is shorting between the adjaecent [sic] un-insulated wire sections.

This statement just begs the question of what caused the insulation to break down in the first place. Heat causes it. The heat has two sources: convection from the hot engine, and voltage drop in the wire. You can prevent convection from the engine by wrapping the harness in fibreglass heat-insulating tape, and you can prevent heating due to voltage drop in the wire by using a larger-gauge wire.

"Excessive heat causes copper to become brittle, usually characterized by a brown appearance and how it breaks easily without its normal flexibility."

Another straw man. That's exactly what I said, but you're trying to make it appear that I said something different. That brittle, brown stuff is copper oxide.

"Boat cable is pre-tinned, easier to work with, less prone to corrosion where exposed, and more flexible which all makes for a better harness and easier for the OP to work with. The normal household THHN etc. will not be flexible enough for automotive use, and the stuff you buy at autozone et al can be of dubious quality."

I never said you shouldn't use good quality wire; just that if you're going to wrap it in fibreglass heat insulating tape, you don't need to use mil-spec or boat wire because it is not going to be exposed to any heat in the first place. For example, I wrapped the headers on my hot rod with fibreglass heat-insulating tape. When the engine was running full-tilt on the dyno and headers were red hot, the heat-insulating tape was only warm to the touch.

"Mercedes didn't use "the smallest gauge wire they could get away with", they used the correct wire gauge"

You're distorting what I said. Yes, they used the correct wire gauge if everything works as it did when it left the factory. But as the factory-stock wire degrades, and when the connectors get dirty, there's no conductivity headroom. That's what I meant by "the smallest gauge wire they could get away with". By using larger gauge wire, you have much more conductivity headroom to prevent excessive voltage drops.

"I'd like to see your voltage-drop calculations on the wiring"

Sure, no problem. The current-carrying capacity of a wire is proportional to its cross-sectional area, which is in turn proportional to its diameter squared. Each AWG gauge has a diameter approximately 1.12 times that of the next smaller gauge. That means that, for example, AWG 16 gauge wire has a diameter 1.25 times as large as AWG 18 gauge wire (because it's two gauges larger). Therefore, AWG 16 gauge wire has a current-carrying capacity of almost 1.6 times (1.25 squared) that of AWG 18 gauge wire before excessive voltage drop is encountered. That's a lot more headroom!

Methinks thou dost protest too much.

So, you're more interested in winning an arguement than helping the OP, I get it. You've really stated nothing new nor addressed the inaccuracies in your former posts.

To the OP: Make the harness out of the OE gauge wire, use good quality automotive or better wire, I suggest boat cable, wrap and run it as original, and you'll be fine just like the millions of Mercedes-Benz harnesses that preceeded and succeeded the bad-insulation years. Fiberglass wraps et al are not necessary nor are over-sizing the wires. Good luck with the new harness, should take a little time and patience.

__________________

Gone to the dark side

- Jeff

I'll be a little diplomat here, both points of view add value to the thread as well as address the OP's concerns.
The point that using good quality original spec wiring would be more than sufficient to last the remaining life of the car is correct and well taken. Though, suggesting the use of materials that exceed spec supplemented with techniques and protection that address conditions that had some affect on the failure are also quite valid, not necessarily incorrect and are certainly worthwhile to point out.
While I would probably opt for the factory spec system (in this case) I'm glad to have learned about the protective quality of fiberglas tape and the explanation of wire gauges will be useful to many readers.

I'm curious though, as I'm not so electrically knowledgeable. Can't over-gauging wire pose a potential threat to some more delicate instruments and sensors? That is, some wire gauges are actually chosen to cap or restrict the flow of juice (provide resistance) and using a larger gauge wire might allow too much amperage to flow though components (particularly computers and control units) that aren't rated for such flow. Maybe I'm wrong about this or maybe it doesn't really apply here, just curious.

Although the wire does technically provide resistance, and reduce voltage, the voltage drop over a few feet of 16AWG wire carrying perhaps 20ma-100ma is negligable. The gauges are calibrated / designed for that voltage drop and could read a very small amount differently with oversized wiring, but for the most part no change, same with the computers.

As far as protection goes, fuses not wires provide that protection.

__________________

Gone to the dark side

- Jeff

I'm a bit late to this party, but bear with me. Rebuilding, the harness may be a weekend event, but what would be the harm in fiberglass wrapping the rebuilt harness? The way I understand it, heat creates resistance ad resistance creates heat...would it hurt to minimize the affects of ambient heat at the get go?

__________________
1993 190E 2.6 135k
1989 Ford Thunderbird SC 5 Spd 79K

Suit yourself on rewiring/rebuilding your engine wiring harness. The risk of engine fire alone would be worth the ~$800 to me, not to mention the aggravation of the car potentially leaving you stranded...

-GH

__________________
For Now:
1992 Mercedes Benz 500SL
1998 BMW 528i
2003 Honda Element
2002 CBR600F4i
1977 Coachmen Motor Home

Thanks babymog. Hmmmm, yep, there are those pesky fuses keeping the juice pretty well under control, aren't there.
Okay , I'm an idiot, but I did admit that i weren't none two 'lectrificly lerned!

Thanks for all the enlightening. In giving this a little more thought, what we do with the harness depends on how long we continue to use this car and how well it performs and how many additional repairs it needs. If we drive this car for, say two more years and all it requires is oil changes and fuel, we might be inclined to opt for a new factory harness just for convenience. If this car continues to rack up repairs or becomes unreliable, it may well just get sold. In reality, the car isn't worth much...a 15 year old mercedes with 115k miles is worth maybe 2500? So spending more than a 3rd of the value of the car on a harness doesn't make sense considering it is a 3rd vehicle anyway. So we will see. I wouldn't mind rebuilding the harness myself but maybe trading for a newer 3rd car (210 benz) is a better bet? I do like having a 'classic' mercedes though.

__________________
________________________
2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro

I just did a quick web check. The boat cable I found is only rated to 105 deg C. http://bestboatwire.com/catalog/default.php/cPath/23 Is that high enough? I would guess not for all locations in the engine, especially in the wiring located right on the engine. Is there a higher temperature spec for boat wire than this?

One of these days I am going to rig my thermocouple reader to monitor engine compartment temperatures at various locations so I can see just what is going on in there. I am just enough of a nerd to do this, too :-P I live in a hot climate so this is a more challenging application than, say, for someone living in the northeast.

That wiring is considered heat resistant, but there are other grades rated higher.
AVX: 100°C
AEX: 120°C
GXL, JXL: 125°C