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  #1  
Old 08-28-2011, 11:26 PM
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’89 300E electrical, vacuum, and mechanical issues

I’m having some issues with my parents’ 1989 300E. I’m basically the permanent driver for the car, so I’d like to fix it up a bit. If anyone has time, I could use some help with some electrical, vacuum, and mechanical issues.

Electrical
Fuse 9 and C appear to have shorts. Fuse 9 has a constant drain on the battery, and fuse C blows intermittently. My parents have paid several thousand dollars before to have them tracked down, and while several have been discovered in places like the rear dome light, the problem persists. Eventually they decided just to ignore it, so fuse 9 stays removed and a blown fuse sits in C.

Fuse 9 controls:
Quote:
Diagnostic term. 6
Hazard warning system
Clock
Front roof light
Radio
Vanity mirror light
Relay comfort circuitry term 86
Fuse C controls:
Quote:
Rear roof light
Trunk light
Rear door locking system
Safety belt handover arm
Seat back arrester
Central locking system
Door lights
Reading lamps
Aut. Antenna
Control unit seat adjustment

In regards to fuse 9:
There is an after-market stereo in the car, and I’m fairly sure I’ve narrowed the short down to that. The radio works fine when the fuse is put in. However, I’m not sure what “diagnostic term. 6” and “relay comfort circuitry term. 86” are, so I can’t test those.

When using a multi-meter to take a reading, there’s a “clicking” sound. It happens only one time when the circuit is completed, but occurs every time without fail.

1. What are “diagnostic term. 6” and “relay comfort circuitry term. 86”?

2. If the radio short is just a bad wire, my parents should be able to help me fix that (they know how to splice wires). However, we're a bit fearful the issue is the wiring is just done incorrectly (wires spliced together that shouldn't touch). Is this a possibility despite the radio functioning with the fuse in?

2.b. If so, does anyone have any wiring guides so we can hook up the after-market radio correctly?

3. Any idea what the clicking sound could be?


In regards to fuse C:
I’m unsure of the cause. Sometimes the multi-meter shows current through it with the car off; other times it reads 0. As such, I’m not sure how to test this aside from unplugging things, putting in a new fuse, and waiting several days to see if it blows.

4. How should I go about looking for the short here?


Vacuum
The AC only comes out the side vents (rather weakly) and through the defroster. Reading from other people’s misfortunes here, I now know this to be an issue with the vacuum pods. I’ve already looked up how to replace them, but would like to confirm the part numbers to make sure the correct ones get ordered.

I found a list here, but those are for an ’87 300D. When we looked up the car then the part number, the numbers we found were:

Quote:
W0133-1631053
W0133-1617283
W0133-1621814
W0133-1622409
W0133-1622876
I’m not sure which part is what though; all I know is that the footwell pod is not included in that list.

5. Which list of part numbers are correct? If the W0133-16… is accurate, what is the number for the footwell pod?

Assuming a replacement footwell pod can’t be found:
6. What does this direct airflow to?

7. Is there some sort of fix I can do on it?


Mechanical
These are mostly vanity, but if I’m already doing lots of work on the car, I figured why not.

The rear passenger door appears to be damaged. The issue seems to stem from the door stop brace. I’m not sure what the actual problem is aside from the door becoming hard to close. My parents are afraid of it getting stuck (to the point we don’t use that door at all).

7. How do I determine what is actually wrong with the door brace?


The cruise control doesn’t work. I’m not sure what the problem is. It seems like the stick is broken. If it were a compass, the stick would always sit in the “south” spot instead of the middle like I would expect. I can move the stick up and forward/back (after moving it up slightly), but it always returns to that “south” position. Nothing happens when moving the cruise control stick around.

8. Is there a guide to removing the cruise control stick and repairing it? I found something on removing part of the wheel and cruise control to fix the turn signal here which I can use to start with, but if there’s a guide about my issue I’d rather use that.


This problem isn’t actually a vanity thing.
We had the transmission fluid changed a few years back, and in the old fluid some metal shavings were found. We were told this means the transmission could die on us at some point, but haven’t had any other problems with the transmission thus far.

9. Anyone else have this problem in the past? Is the transmission likely to die on us?



-Hope Remains

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  #2  
Old 08-29-2011, 09:34 AM
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Wow!

As far as the electrical issues go...I like to divide & conquer.

I always get to the bottom of the fuse box & install in-line fuse holders to each of the wires that go to each circuit & install a smaller fuse than in the main fuse holder.

Whichever circuit blows that smaller fuse, bingo!
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  #3  
Old 08-30-2011, 09:18 AM
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Fuse 9

You mentioned a previous problem with the rear dome. The clicking noise was probably the related to the dome lighting circuit and the comfort relay system that delays the dome lights from turning off for a few seconds after the doors are closed. The noise comes from under the dash right about where the driver's right knee would be.

Try taking the blub out of the rear dome and see if that fuse still blows. I suspect the short is still in the dome lighting system but it could be the radio too since it was replaced.
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  #4  
Old 09-06-2011, 10:19 PM
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Quote:
Originally Posted by mbdoc View Post
Wow!

As far as the electrical issues go...I like to divide & conquer.

I always get to the bottom of the fuse box & install in-line fuse holders to each of the wires that go to each circuit & install a smaller fuse than in the main fuse holder.

Whichever circuit blows that smaller fuse, bingo!
How do I then determine what specifically the smaller circuit goes to?
Where can I acquire a small in-line fuse holder? Pretty much any electronics store?


Quote:
Originally Posted by big dog 2 View Post
You mentioned a previous problem with the rear dome. The clicking noise was probably the related to the dome lighting circuit and the comfort relay system that delays the dome lights from turning off for a few seconds after the doors are closed. The noise comes from under the dash right about where the driver's right knee would be.

Try taking the blub out of the rear dome and see if that fuse still blows. I suspect the short is still in the dome lighting system but it could be the radio too since it was replaced.
Aren't the rear dome light and relay comfort circuit on two different lines?



Any other suggestions on the other issues?


-Hope
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  #5  
Old 09-07-2011, 08:21 AM
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Location: Tucker, Ga USA
Posts: 12,153
You will KNOW what blows the smaller fuse, as something on that fuse will quit working.

Most auto part stores have in-line fuse holders as well as radio shack
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Mercedes Benz Star Technician (2 times)
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27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
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  #6  
Old 09-07-2011, 10:10 AM
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Check out Supplement 11 page 5 for Additional Electrical Troubleshooting procedures on 124's: Supplement 11

Tried to upload to post but received error message:
Your file of 763.1 KB bytes exceeds the forum's limit of 732.4 KB for this filetype.
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  #7  
Old 09-19-2011, 01:16 PM
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Posts: 10
EDIT: Scratch that entirely.
The old antenna was actually unplugged, so the short on Fuse C is either in the antenna button or elsewhere in the car. Also, the old antenna is different from this new one I was given to install, so I didn't swap them out.
After leaving the battery connected for about two hours, the battery was dead, so a short still exists on Fuse 9.

Guess I'll be doing an in-line fuse holders after all.
On that note, when I looked under the fuse box, I was a bit confused on how to go about installing an in-line fuse holder. Any directions on how to do it?

END EDIT


Quote:
Originally Posted by mbdoc View Post
You will KNOW what blows the smaller fuse, as something on that fuse will quit working.

Most auto part stores have in-line fuse holders as well as radio shack
Oh...duh...well I feel silly.
I think I've found the problem on Fuse C without getting an in-line fuse holder though; read below.


I just finished changing vacuum pods yesterday and got the dash put back together. While working on the car, I redid some shoddy tape on the spliced after-market stereo wiring and taking out/putting back the rear dome light (both are part of Fuse 9). I decided to check the current on both Fuses C and 9 and got nothing.

The after-market stereo wiring and rear dome light could have been the issue for 9...time will tell for sure.

In regard to fuse C, I didn't mess with anything on that circuit. I began checking things out, and it seemed things were working fine until I tried putting the antenna up. Nothing happened at all. Tried pushing the switch up and down without any effect. I turned the car off and checked the fuse to find it blown. At this point, my dad mentions two things:
1. We happen to have an new Mercedes antenna for the car. At some point my mom apparently bought it, but it was never used.
2. The antenna was changed before while we were having issues with this fuse. For about a month everything worked fine, but then the fuse began to blow again.

I recall reading somewhere on here that the antenna can be a source of shorts, but was unable to find any threads about it.

I plan on replacing the antenna to see if it's the issue, but if the fuse blows again, how do I go about checking the wiring to the antenna? The wiring where it plugs into the antenna looks fine.


-Hope

Last edited by Hope Remains; 09-19-2011 at 09:43 PM.
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  #8  
Old 09-24-2011, 09:00 AM
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Posts: 3
Hi
I am pretty confident that your problem is due to one/several of your doors and/or trunk courtesy light wires. The intermitence is due to the fact that the insulation breaks at the hinges and the plus (rd/br I think) and minus wires for the bulbs touch intermittently at first. Eventually they melt and stick together (messy). Everytime you open the offending door/s you ground the minus wire and bam!
First, disconnect all door switches, carefully dress the wires, fuse C should not blow.

Remove the bulbs and look for intermittent or permanent 7 to 12 volts on the minus wires. Note: It is normal to have + DC on the minus wire (through the bulb filament) until the door open and the wire is grounded, so you must remove the bulbs and door switches in order to isolate it from either ground or B+! If there still is voltage on it, there is a short (usually intermittent).

You will then have to remove the door's panels for further inspection of the wires at the hinges. Beware as there may be more than one of them.

One more thing: some people just move on as soon as they fix their problem. Please post your experience to help others as I just did now
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  #9  
Old 10-22-2011, 11:38 PM
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Posts: 10
This above appears to be my problem. It's the front passenger door. It looked like the issue was the area right next to the courtesy light, but through an accident I discovered there was another short in the wires by the hinge. When the door is almost closed all the way, the key alarm goes off and courtesy lights dim.
I pulled off the plastic panel by the right passenger foot to get a better idea of how to get to the wires, and saw insulation that had split open causing lots of wire to be exposed.

Now the problem is: I have no idea how to get to that wire.
I removed the door panel, but that didn't open up any ways to pull the wire out.

How do I remove the wires that run from the door into the car? Given how bad the wire is, I expect everything nearby will need doctored up with electrical tape.


-Hope
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  #10  
Old 10-27-2011, 10:28 PM
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Removing the plastic to the right of the passenger footrest will expose one end of the wiring which once disconnected from the light, can be gently pulled inside the car.
let me know how you are doing
les
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  #11  
Old 11-08-2011, 10:19 AM
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Posts: 10
Since I didn't know where the wires went to inside the car and what wiring harness to order, I had a mechanic fix this problem.


-Hope

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