battery draining electrical hodge podge - Mercedes-Benz Forum
LinkBack Thread Tools Display Modes
post #1 of 4 (permalink) Old 07-31-2018, 10:14 AM Thread Starter
BenzWorld Newbie
Date registered: Jul 2018
Vehicle: '81 240d '84 3
Location: texas
Posts: 2
Mentioned: 0 Post(s)
Quoted: 0 Post(s)
(Thread Starter)
battery draining electrical hodge podge

I have a '84 300sd with a hard to find parasitic drain on the battery. I've tried finding it with a ammeter by removing the fuses one by one without any luck. The PO did lots of odd electrical "work" on it .There's lots of electr ical stuff on this model so lots of places for problems. So far I've found that tha diodes in the alternator are burned. If I unplug the wires from the back of the alternator, there should be no drain from the alternator but there still is one. With a milliamp meter across the negative terminal and the cable there is a strong pulsing drain on the battery.I'm wondering what would cause a drain and generate a pulse like a ticking clock. I've tried all the fuses I can find. My main questions are: could the alt be causing the problem even with the wires disconnected? What electrical devices on this car would generate an electrical pulse? Thanks for any advice.
madill is offline  
Sponsored Links
post #2 of 4 (permalink) Old 07-31-2018, 11:06 AM
BenzWorld Elite
rumb's Avatar
Date registered: Oct 2012
Vehicle: 68 250S, 91 300se, 98 SL500, 450SEL 6.9, 14 CLS550 Past MB's; 300SD, 300E, 300TE, 190E, ML420
Location: Fort Collins, Colorado
Posts: 3,990
Mentioned: 19 Post(s)
Quoted: 830 Post(s)
If the alternator is disconnected then it cant be drawing anything.
try looking at the warning flasher/turn signals.

also under the passenger carpet is the alarm system, unplug it.
rumb is online now  
post #3 of 4 (permalink) Old 07-31-2018, 11:48 AM
BenzWorld Veteran
ejboyd5's Avatar
Date registered: Jun 2009
Vehicle: 1955 300 SL
Location: Southold, NY
Posts: 626
Mentioned: 1 Post(s)
Quoted: 173 Post(s)
Remove the flasher unit(s) to see if that eliminates the drain. Since the 4-way hazard flasher is wired to be always "hot," many tend to use it as a source of power when adding aftermarket accessories, If you have removed all the wires from the alternator you have eliminated it as the problem.
ejboyd5 is offline  
Sponsored Links
post #4 of 4 (permalink) Old 07-31-2018, 10:03 PM
Lifetime Premium Member
4DGeorge's Avatar
Date registered: Jan 2018
Vehicle: 2006 S500 (W220, Designo Espresso, AMG Sport, LWB)
Location: Houston, Texas, USA
Posts: 312
Mentioned: 15 Post(s)
Quoted: 41 Post(s)
Lifetime Premium Member
When pulling the fuses out, you may want to keep pulling until they're all out - instead of putting each one back before pulling the next.
The PO may have wired something to two power sources (one switched, one always hot). I've seen this most often on alarm, audio, and auxiliary lighting.

The pulsing you're registering could be a capacitor charging and discharging (like when an amplifier is turned on and off).

What about flood damage?

Sent from my SM-N950U using Tapatalk
4DGeorge is offline  
Sponsored Links

  Mercedes-Benz Forum > Mercedes-Benz Sedan Forums > W126 S,SE,SEC,SEL,SD,SDL Class

Quick Reply

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


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

Email Address:


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

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