[W126 Coupe] electrical expertise needed

Wed Sep 14 12:02:17 EDT 2005

 Hi "figster"... I am trying to test my annoying clock, that sometimes works, sometimes doesn't.  If you remember the recent post by Dick Spellman pointing me to the BenzStore that rebuilds them, they told me that clocks are testable by hooking 12v to the spade connector on the back of the clock and grounding the clock.  Also see Dick's email earlier today talking about connecting the clock with wire leads to + and - of the battery for testing purposes. Now, why test it this way?  Well, because the clock acts flaky, that's why.  I don't want to waste money shipping it somewhere to have them tell me its not broken and then ship it back.  So I am trying to test it on my own first to see if it really works.  If it does, I know the problem is in the wiring in the car, either the power to the clock wire is flaky, or the ground that it uses is flaky.  As to the clock itself, there aren't that many components.  I've been told the capacitors go bad, but when I talked to the BenzStore

they said that if those go, "usually" the clock just stops working and that's that.  But mine works fine for a day or two, then suddenly stops, then starts up again when it feels like it, and so on.  Dick suggested maybe the adjustment mechanism is sticking but that only makes sense if I touch it and adjust it.  I can do NOTHING and the clock will work or stop as it feels like.  So I'm trying to debug this situation without spending tons of money and do things logically.  I'm not trying to hook up anything permanently, I wouldn't go that far on my own for sure!  Just debugging. Thanks,Markus--- On Wed 09/14, a figment of the imagination &lt; figstir at yahoo.com &gt; wrote:From: a figment of the imagination [mailto: figstir at yahoo.com]To: mfmeyer at iwon.com, mbcoupes at mbcoupes.comDate: Wed, 14 Sep 2005 08:39:33 -0700 (PDT)Subject: Re: [W126 Coupe] electrical expertise neededHey 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 iselectrical ground, which is closer to a negative leador terminal. In these W126 bodies, Mercedes-Benzengineers have done a great job of color coding allthe wiring. Brown wires without any stripes aregenerally ground, which I would call closer to an"electrical ground" or one that goes directly to thenegative terminal of the battery. I've tried both types of grounds when debugging,diagnosing, and re-wiring or modifying tons ofelectrical stuff in my SEC. The best ground to use isone off the brown wires. There are several commoncontact points for this throughout the car. One greatone is right behind the instrument cluster. Anotherone sits behind the stereo deck.Regarding direct connections to the battery. This isa "no no"! First, you are playing with 12 volts DC. While thismay not seem dangerous to you, it can be. It isdirect current and you can pull as many Amps as 
yourresistance/impendance will allow you to. As anexample, this could be as high as 15-25+ Amps (hencethe fuse ratings), which could theoretically kill you,if not give you a great big jolt. I have only to tellyou that I have experienced some level of it and I'lltell you that it hurt bad and had me using rubbergloves from that point further, despite my experienceand talent. Second, you don't want to directly connect to thebattery because you can not only short-circuit theelectronics you are working with but you could alsocreate a hazard for a nice electricalfire!...obviously, right in the engine compartmentwith its rich sources of fuel, air, etc... Third, it's simply bad etiquette to wire anythingdirectly to the 12-volt battery; it looks bad...like aserious hack job.....of which I would immediately shyaway from, if you were to ever resell your car. Fourth, the wire you may be using may not be able tohandle the current directly from the battery. Manypeople don't understand 
wiring ratings (thickness,length, conductivity, strands, shielding, etc..). Ifyou use the wrong one, you can create a source of anelectrical fire. Fifth, you would always want to make sure you have anin-line fuse rated for the max amps of your testingdevice and in some cases an electrical relay to trapfast spikes! This is why there is a fuse box withfuses and relays! Consequently, I highly recommend that you pick off12-volts from somewhere within the W126 body and thatyou use the solid brown wires as you're ground. WhatI have found is that the bright red and white stripedwires are a hot continuous 12-volts. Theyellow-black stripped wires supply "ignition key"switched-on 12-volts; that is, after you have put thekey in the ignition and turned it one notch, withoutcranking over the engine, you get current. I wouldrecommend that you use this wire, but test it firstwith a volt-meter.Always, use proper testing equipment before directlyconnecting to any device. Finally, in general, 
I don't recommend that you playwith electronics. It would be best to find aspecialist to do the work for you, because you will beextremely upset if you were to damage anything due toeither my suggestions or work of your own, even byaccident, which can happen easily. It is frustratingand often hard to tell what has gone wrong andrequires great debugging and problem-solving thinkingskills. Again, this is electronics and it takes yearsof experience and physics/engineering study andpractice to really understand what you are doing, howthe system was designed, and to use test equipment andto diagnose and debug problems you encounter along theway. Most kids at audio shops, as well, do not havethis experience and may tell you things that areblatantly wrong, by-passing common sense or physics,leading to a short-circuit or electrical fire later onafter the work is done or something else. I know thisalso from experience in believing these kids were more"experienced" and knowledgeable" 
than me, even despiteplaying with electronics since I was a 7-years old andstudying it formally at a pre-eminent school. Sometimes they are correct, but they stay withinlimited bounds, which allows them success, as an apprentice, and that's good for the limited stuff theydo. This may be all that you need depending on whatyou are doing. In general, if you are extremelycareful and have great understanding of everything,you should be successful.Please tell us what you are testing or trying tohook-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 electronicsaka, fig__________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.comThe MB Coupes Website!W126 SEC Mailing ListPostings remain property of MB Coupes, L.L.C.

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