FW: Re: [W126 Coupe] electrical expertise needed

[Mister McGoo]

>From: a figment of the imagination <figstir at yahoo.com>
>Reply-To: figstir at yahoo.com,Mercedes Coupes Mailing Lists 
><mbcoupes at mbcoupes.com>
>To: mfmeyer at iwon.com,Mercedes Coupes Mailing Lists <mbcoupes at mbcoupes.com>
>Subject: Re: [W126 Coupe] electrical expertise needed
>Date: Wed, 14 Sep 2005 08:39:33 -0700 (PDT)
>
>Hey Markus:
>
>Electrical stuff is my specialty, so I'll try to help.
>This is a simple, abbreviated explanation.
>
>Basically, there are two types of ground.  First,
>there is ground, such as the chasis.  Second, there is
>electrical ground, which is closer to a negative lead
>or terminal.  In these W126 bodies, Mercedes-Benz
>engineers have done a great job of color coding all
>the wiring.  Brown wires without any stripes are
>generally ground, which I would call closer to an
>"electrical ground" or one that goes directly to the
>negative terminal of the battery.
>
>I've tried both types of grounds when debugging,
>diagnosing, and re-wiring or modifying tons of
>electrical stuff in my SEC.  The best ground to use is
>one off the brown wires.  There are several common
>contact points for this throughout the car.  One great
>one is right behind the instrument cluster.  Another
>one sits behind the stereo deck.
>
>Regarding direct connections to the battery.  This is
>a "no no"!
>
>First, you are playing with 12 volts DC.  While this
>may not seem dangerous to you, it can be.  It is
>direct current and you can pull as many Amps as your
>resistance/impendance will allow you to.  As an
>example, this could be as high as 15-25+ Amps (hence
>the fuse ratings), which could theoretically kill you,
>if not give you a great big jolt.  I have only to tell
>you that I have experienced some level of it and I'll
>tell you that it hurt bad and had me using rubber
>gloves from that point further, despite my experience
>and talent.
>
>Second, you don't want to directly connect to the
>battery because you can not only  short-circuit the
>electronics you are working with but you could also
>create a hazard for a nice electrical
>fire!...obviously, right in the engine compartment
>with its rich sources of fuel, air, etc...
>
>Third, it's simply bad etiquette to wire anything
>directly to the 12-volt battery; it looks bad...like a
>serious hack job.....of which I would immediately shy
>away from, if you were to ever resell your car.
>
>Fourth, the wire you may be using may not be able to
>handle the current directly from the battery.  Many
>people don't understand wiring ratings (thickness,
>length, conductivity, strands, shielding, etc..).  If
>you use the wrong one, you can create a source of an
>electrical fire.
>
>Fifth, you would always want to make sure you have an
>in-line fuse rated for the max amps of your testing
>device and in some cases an electrical relay to trap
>fast spikes!  This is why there is a fuse box with
>fuses and relays!
>
>Consequently, I highly recommend that you pick off
>12-volts from somewhere within the W126 body and that
>you use the solid brown wires as you're ground.  What
>I have found is that the bright red and white striped
>wires are a hot continuous 12-volts.   The
>yellow-black stripped wires supply "ignition key"
>switched-on 12-volts; that is, after you have put the
>key in the ignition and turned it one notch, without
>cranking over the engine, you get current.  I would
>recommend that you use this wire, but test it first
>with a volt-meter.
>Always, use proper testing equipment before directly
>connecting to any device.
>
>Finally, in general, I don't recommend that you play
>with electronics.  It would be best to find a
>specialist to do the work for you, because you will be
>extremely upset if you were to damage anything due to
>either my suggestions or work of your own, even by
>accident, which can happen easily.  It is frustrating
>and often hard to tell what has gone wrong and
>requires great debugging and problem-solving thinking
>skills.  Again, this is electronics and it takes years
>of experience and physics/engineering study and
>practice to really understand what you are doing, how
>the system was designed, and to use test equipment and
>to diagnose and debug problems you encounter along the
>way.  Most kids at audio shops, as well, do not have
>this experience and may tell you things that are
>blatantly wrong, by-passing common sense or physics,
>leading to a short-circuit or electrical fire later on
>after the work is done or something else.  I know this
>also from experience in believing these kids were more
>"experienced" and knowledgeable" than me, even despite
>playing with electronics since I was a 7-years old and
>studying it formally at a pre-eminent school.
>Sometimes they are correct, but they stay within
>limited bounds, which allows them success, as an
>apprentice, and that's good for the limited stuff they
>do.  This may be all that you need depending on what
>you are doing.  In general, if you are extremely
>careful and have great understanding of everything,
>you should be successful.
>
>Please tell us what you are testing or trying to
>hook-up.  If there is a way, I can help let me know.
>I can be briefer, if I know more specifics.
>
>-figment of high-tech electronics
>aka, fig
>
>
>
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