84 300D Battery loses charge very fast - Page 2 - PeachParts Mercedes-Benz Forum

benhogan · #16 03-16-2010, 09:30 AM

Quote:

Originally Posted by ah-kay

Make sure you have a FULLY charged and good battery and do the followings with a DMM:

1) With the car running. Check the voltage of the battery terminal. It should be normal 13-14.4V. This verifies the alternator is working.
2) With the car off and all lights, radio off. Remove key. Disconnect -ve terminal and measure any current draining the battery. It should be mininal < 500ma. The residual current is for clock or alarm etc.
3) If it draws a lot of current then go the fuse box and remove each fuse then measure the current across the fuse terminal. Most should have 0 current, except the fuse to the dash (it should be small also ).
4) If there is a massive short somewhere then there may be a burning smell.
5) If there is a short then the fuse would blow unless the fuse is over-rated.
6) I have resolved a lot of shorts in this manner.

Good luck.

+1
the above procedure is perfect.

Nick300cd · #17 11-06-2013, 03:40 PM

So what happened? I'm having the same symptoms with my 82 300cd. Still no resolve for me.

TnBob · #18 11-06-2013, 06:30 PM

For those using the well laid out and proper test procedure, remember that if you are going from the negative terminal to ground, the meter black lead goes on the battery cable and the red to ground.

Your clock will cause the meter to jump to about 50ma each second as it ticks.
IF ... everything else is off, that is about the max you should read, 50 milli amps.

If you want to see what your glow plug relay draws you will need a better meter.