'81 300SD ignition switch

Hi all, I picked up an 81 300SD that had ignition switch problems. To get the air conditioner to work, you had to wiggle the key. Ok, no problem, replace the
ignition switch... After hours of messing with it, I finally got it replaced and everything worked fine... for one day. I then had to wiggle the wiring plug to get anything working the next day, now nothing works. I cleaned up the old switch, and it worked fine... for a couple of starts. I took the new switch apart, and found that one of the contacts had over heated, and no longer made contact. So now I am trying to figure out the wiring on it so I can try and chase down the problem. I have a chilton manual, but with it I can only determine the following wires The two 30 terminals are the hot leads into the switch The Vio/wht is to the Starter and glow plug control relay The red/blk is to the glow plug relay... Is there a better source for wiring diagrams available online anywhere? Is there some common problems with the ignition switch in these models? Any pointers or help would be a big help.
Thanks, Bret
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This reply may, or may not, help you. Its from the wiring diagram of my 1980 (116) 300SD - different year so beware.
Switch ID    Wire Color(s)    Destination
50        violet/white    A/C Relay Starter 15        red/black    power to fuses 8 & 16 15        red/black    power to fuses 8 & 16 R        red/green    radio 30        red        headlight switch 30        red        headlight switch (space on the diagram) P        green/white    headlight switch P30        red/green    from fuse #1
That's as far as I can take this information. Remember, you model may differ.
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80 had a servo system which does not pull as many amps from the ignition switch.
81 has circuit 15X from from the ignition switch that is a dedicated power to the ACC blower. More than likely, this is your overheated contact? If yes, check the amp draw of your blower motor.
And what is the MB part number on your replacement ignition switch? [just the 1st 3 numbers]
"-->> T.G. Lambach <<--" <"T.G. Lambach at NoHamorSpamcomcast.net"> wrote in message

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Now that I have the switch out in the daylight, I can see the plastic melted on the new switch around the 15X post. Is this a common problem? Could it be from starting the car with the AC on? I got the new switch from 'performance4Benz, and it doesn't have the number stamped on it. I did wonder if it was the correct switch when I saw that it didn't have the plastic 'T' that locks the wire plug on. It did have the same numbering on the posts, and the same pattern. Where can I get a 'good' manual for this car? I need good wiring diagrams, vacuum diagrams, etc What manual would you suggest? paper or CD?
Thanks Bret

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Check the amp draw of your blower motor. Too many amps will melt the connector. No part number on the ign switch electrical section tells me it is a cheapo knockoff. Go to your local MB dealer and buy a real one! The original switch was part number 126 462 00 93. It was replaced by part number 124 462 00 93. The newest switch is part number 202 545 01 04. The new ones no longer have the anti-theft T. The turning resistance was too much on the 126 and 124 switches. This caused the aluminum drive to shear off on the 124 and 201 body steering locks.
Best info out is the real Mercedes workshop manual on CD. Part number P-2700-126-099 (version 1.1) Suggested list $19.99
Order from your local dealer or call 1-800-FOR-MERC

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Karl, Thanks for the detailed help. I will be ordering the manual and new switch today. What should the amp draw be for the blower motor? My ammeter can only handle up to 10A.
Thank again Bret

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On startup at high speed, it will draw the most. Running on high speed it will draw almost 25 amps. Using the law of friction, it takes twice as much energy to get something moving as it does to keep it moving.

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