Need info on a ballast resistor - Mercedes-Benz Forum

 
LinkBack Thread Tools Display Modes
post #1 of 7 (permalink) Old 11-17-2012, 08:47 AM Thread Starter
BenzWorld Member
 
Luna Gaudi's 72 250's Avatar
 
Date registered: Sep 2012
Vehicle: 1972 Mercedes Benz 250
Location: Santa Fe, NM U.S.A.
Posts: 389
Mentioned: 0 Post(s)
Quoted: 17 Post(s)
(Thread Starter)
Need info on a ballast resistor

1972 250 /8 W114

So there are two ballast resistors right behind the battery (between the battery and firewall) I know that the 0.6 goes to the coil and I'm pretty sure
that there are no problems with that one, but the other resistor that is in there is a BERU WZ 04-2 0.4 and I would like to know if this is the correct one that is supposed to be installed in there and what is the purpose of this second resistor? If this is the correct ballast resistor, how can I test it to see that it is working correctly? Here is the issue that I am having. This second resistor has two wires on one side and one wire on the other side (I have not determined yet what these wires are for)

I was diagnosing why the horn wasnt working.

Here is what happened... The horn wouldn't work with the key NOT in the ignition, so I inserted the key and turned it to the second position (engine not running) and horn started working then after about a thirty seconds the horn wouldn't work anymore, I went to check fuse number 2 and noticed ALOT of heat coming from the two ballast resistors, I turned the key off and disconnected the negative battery terminal. I know theses resistors are supposed to get hot, but when I sprayed them with a water bottle the water sizzled right off like it would on a newly welded piece of steel. After several sprays of water to the point where the resistor wasn't sizzling anymore, I immediately connected the negative battery terminal, turned the key on to position 2 and tried the horn again and it worked. How can these be related? Also, I thought that the horn was supposed to work at all times (key not in ignition) Is my horn wiring all wrong? Is there a horn relay on this model? Also, is there a way to test the ballast resistor? Does it need to be tested under load? Any thoughts and ideas would be appreciated. Thanks!
Luna Gaudi's 72 250 is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old 11-17-2012, 10:16 AM
BenzWorld Extremist
 
NorCalSL's Avatar
 
Date registered: Jun 2007
Vehicle: '70 280S-'73 450SLC-'81 380SL-'84 500SEC Euro-'92 300SL24-'95 E320
Location: Northcoast of Ca in Eureka
Posts: 985
Mentioned: 0 Post(s)
Quoted: 22 Post(s)
I can't help with the resistor issue, but I can tell you that the horn will not work when the ignition is off. Your horn wiring is ok as far as that goes.
dws


1973 Mercedes 450SLC (PineGreen/MahoganyLeather)
1981 Mercedes 380SL FORSALE (LtIvory/PalominoMBTex)
1984 Mercedes 500SEC Euro (040Black/BlackLeather)
1992 Mercedes 300SL-24 Signal Red/Black Leather
NorCalSL is offline  
post #3 of 7 (permalink) Old 11-17-2012, 12:13 PM
Lifetime Premium Member
 
Date registered: Sep 2008
Vehicle: 1975 450SL
Location: Phoenix
Posts: 2,432
Mentioned: 2 Post(s)
Quoted: 15 Post(s)
Lifetime Premium Member
The resistor that goes to the coil "tunes" the voltage and current for the optimal spark at the plugs. The other resistor is in line with the starter activating circuit, to "tune" the current for the starter components.

Trying not to get technical, it could put someone to sleep that has just finished a pot of coffee.

Scott

Remember: It's not just a car. It's an Adventure.
RadioTek is offline  
post #4 of 7 (permalink) Old 11-18-2012, 08:15 AM Thread Starter
BenzWorld Member
 
Luna Gaudi's 72 250's Avatar
 
Date registered: Sep 2012
Vehicle: 1972 Mercedes Benz 250
Location: Santa Fe, NM U.S.A.
Posts: 389
Mentioned: 0 Post(s)
Quoted: 17 Post(s)
(Thread Starter)
Thanks for the info guys! Can someone tell me if there is a horn relay, and if there is, where is it located?
Luna Gaudi's 72 250 is offline  
post #5 of 7 (permalink) Old 11-18-2012, 12:21 PM
BenzWorld Member
 
Date registered: Apr 2012
Posts: 115
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by RadioTek View Post
The resistor that goes to the coil "tunes" the voltage and current for the optimal spark at the plugs. The other resistor is in line with the starter activating circuit, to "tune" the current for the starter components.

Trying not to get technical, it could put someone to sleep that has just finished a pot of coffee.

Scott
Huh? What? Tune the voltage?

The resistors simply reduce the voltage (depending on the key position). There is no mystery to a resistor, and the voltage isn't variably set ("tuned") based on other parameters.

The voltage is reduced to prolong the life of the points (the perennial weak link in the traditional ignition chain of components), and I would disagree that the reduced voltage is somehow "optimal" for the plugs based on pretty much on no other manufacturer trying to reduce voltage/spark and everyone trying to get "hotter/better/more" spark.

The SL 113 site has diagrams and an explanation as to why MB included resistors. Pagoda SL Group Technical Manual :: Electrical / TransistorIgnition

Get rid of your points, and with a proper coil to match the ignition system you choose, you can eliminate the resistors and get full voltage at the coil (and hence more energy at the plugs).

YMMV/IMHO/CYA/ETC/
Palolo is offline  
post #6 of 7 (permalink) Old 11-18-2012, 12:46 PM
Lifetime Premium Member
 
Date registered: Sep 2008
Vehicle: 1975 450SL
Location: Phoenix
Posts: 2,432
Mentioned: 2 Post(s)
Quoted: 15 Post(s)
Lifetime Premium Member
I was trying not to get technical. The resistor in line with the coil creates a specific voltage/current profile for the best spark. Bosch was one of the pioneers of using a coil with a significantly higher number of windings to create a better spark. When changing the characteristics of the coil, there has to be an added resistance to optimize the current output. The modern coils include the resistance internally, rather than the "1st generation" type system that Bosch pioneered. Maybe Bosch wanted to keep their options open to customize the spark characteristics for various engine, fuel, and country considerations. After all the US was one of the first instigators of pollution control systems on engines, other countries could be using different fuel octane ratings, spark plug heat ranges, etc.... While Bosch was designing for a worldide market.

Like I said, getting technical can be dangerous for the unprepared.

Remember: It's not just a car. It's an Adventure.
RadioTek is offline  
post #7 of 7 (permalink) Old 11-18-2012, 08:05 PM Thread Starter
BenzWorld Member
 
Luna Gaudi's 72 250's Avatar
 
Date registered: Sep 2012
Vehicle: 1972 Mercedes Benz 250
Location: Santa Fe, NM U.S.A.
Posts: 389
Mentioned: 0 Post(s)
Quoted: 17 Post(s)
(Thread Starter)
Well, after I cleaned all the contacts on the resistors and the wires that were connecting to them, it seems as though everything seems to be working again. Was able to take the benz out on a short trip to the gas station today and I have to tell you, it is running very, very good! I am planning on getting it registered this week. The work is about 95 percent completed. Pictures will be uploaded sometime this week. Its been a long two months! but truly a labor of love. Thanks to everyone who has taken the time to respond to all of my questions.
Luna Gaudi's 72 250 is offline  
Sponsored Links
Advertisement
 
Reply

  Mercedes-Benz Forum > General Mercedes-Benz Forums > Vintage Mercedes-Benz

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Mercedes-Benz Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











  • Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
     
    Thread Tools
    Show Printable Version Show Printable Version
    Email this Page Email this Page
    Display Modes
    Linear Mode Linear Mode



    Posting Rules  
    You may post new threads
    You may post replies
    You may not post attachments
    You may not edit your posts

    BB code is On
    Smilies are On
    [IMG] code is On
    HTML code is Off
    Trackbacks are On
    Pingbacks are On
    Refbacks are On

     

    Title goes here

    close
    video goes here
    description goes here. Read Full Story
    For the best viewing experience please update your browser to Google Chrome