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  #1  
Old 05-24-2002, 01:38 AM
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Question Vacuum Locks -- fixed, but now a WEIRD problem

First -- yes, I searched and read it all.

I do not think I have a leak -- they worked perfectly, and quickly, then...not at all.

I was doing some work at the aktive bass amp in the trunk and thought I had crossed a wire (blown a fuse) but the stereo kept on going so I figured I hadn't blown a fuse. An hour later, the locks were found to not be working.

I do not hear a pump whirring at all.

NOTHING else is out on the car (electrically). Could this be a fuse of the vacuum pump? It is dark and I can't check until tomorrow.

By the way, it won't work on either door or the trunk lock, or from inside the car.

(Left door speaker went out, that is why I was at the amp. All connections were good. Any ideas?)

Thanks, brookspw
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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
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2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
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Last edited by brookspw; 05-24-2002 at 10:30 AM.
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  #2  
Old 05-24-2002, 10:33 AM
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Well, once the daylight shined in -- it was the #12 fuse.

BUT, now if I take the key out of the ignition the stereo still plays.

It continues to play (have power) while the doors are opened and ONLY shuts off once I closed the doors.

Was it supposed to be this way all along (I know some new cars do this) or do I have some weird electrical problem?

brookspw
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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles
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  #3  
Old 05-24-2002, 01:14 PM
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Stands to reason that you have two way connection through the power seat diode V1. This is a two pole device located in the fuse box. It will connect fuse #9 which is hot all the time to fuse 2 which is connected to fuse 1 and that should only be hot with the key on.

Its purpose is to separate the ability to work the seats with the door open from common circuits (when acting properly as a one way device [Diode]).
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Continental Imports
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  #4  
Old 05-24-2002, 01:32 PM
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That sounded like it should make sense, but you lost me on the power seat issue.

Please restate for a lesser non-pro tech.

Thanks a bunch,
(so the stereo shouldn't be staying on, I take it?)
Phillip
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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles
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  #5  
Old 05-24-2002, 02:18 PM
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No the radio should go off with the key.

You will need a wiring diagram to follow the logic. It will be easier to just pull the diode and check it. Diodes are checked with an ohm meter. They should look like a short circuit one way and an open circuit the other way.
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  #6  
Old 05-24-2002, 05:14 PM
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First -- I really appreciate the help. You've helped before.

Are you saying that the diode is bad, or that I have something hooked up incorrectly?

Where is this diode, and how should it read on my multimeter?

Otherwise, all I did was replace the #12 fuse.

Thanks,

brookspw
__________________
1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles
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  #7  
Old 05-24-2002, 06:40 PM
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I am saying that if the diode is shorted that the condition you have could exist. The diode is inside a black plastic shell. It is a little bigger than a two prong fuse and it has the same round connector pins as MB relays do. It is located at the back of the relay section of the fuse box (requires removing screws to take off second cover). The absolute left rear corner.

As I said above it will look like a wire in both directions with an ohm meter. A proper diode will have high resistance one direction and low resistance the other direction. It acts as a gate alllowing current to flow in only one direction.
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  #8  
Old 05-24-2002, 07:01 PM
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I spent a lot of time looking for this diode on my 190D. I tried and tried to unbolt the electrical center (fuse box) and reach underneath. I couldn't get it done. It wouldn't lift high enough and I was reluctant to start pulling the wiring harness plugs. In the end I jury rigged a diode to simulate the effect of my blown diode. I later learned that you can reach this diode by reaching up behind the dash after removing the panels below the dash and above the foot well.

I'm a chemical engineer not a EE but I think the normal failure mode for a diode is to fail open not short. If that's true this diode may not me the problem. Good luck!
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  #9  
Old 05-24-2002, 07:18 PM
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Yes an open diode surely wouldn't be the problem. An open diode would not let the seats be controlled with the door open key off.

I can tell you lots of things it won't be.
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  #10  
Old 05-24-2002, 08:22 PM
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Well, I appreciate the help, guys.

I test it by leaving the doors open with the key off (so I can hear the radio on) and then going through all the fuses, jiggling wires, etc. looking for the radio to go off. Of course, if I remove fuse #13 it goes off. If I remove #12, it goes off too. That is the one that blew and caused my door lock problem. My replacement of that one is when this whole thing started.

Strangely enough, when testing this (and touching nothing) sometimes the radio will cut off and on (like you are wiggling a wire with a short).

To sum up -- an open diode won't let this happen (door open key off, seats DO work). Are you saying then, that this may NOT be it?

Thanks, brookspw
__________________
1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles
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  #11  
Old 05-25-2002, 10:29 AM
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Diagnostics is the sum total of experience and conception.

Experience leads us to the reply: it's a blue car so it must be the Battery. Experience also leads us to which end of the wire to start on.

Conception is what one uses in ones mind to assemble all the pieces and dream of a condition that could cause an occurance.

You stated a condition: that your radio kept playing if your doors were left open with the key turned off. Experience tells me that there IS a system that changes on/off capabilities naturally with the door opening. That system is the power seats. They work with the key off; when the door is opened but not if closed (then the key must be turned on.

In my case, experience also tells me that the diode that allows this to happen does fail in ways that turns certain circuits on that shouldn't be. SOOOOOOOOOOOOOOOOOOOOO, in your case I conceived that this could happen and I went to my wiring diagram and verified that a shorted diode would power fuse #1 which is the one that turns the radio off with the key. My diagnostic job is done. I have hypothesized an exact condition that can cause such an event. The next step is to validate the hypothesis.

If I were working on the car, I would have done the hard work at this point (by confirming with research that the circuitry is right for my hypothesis). The easy job of verification has to be left to you (you have the car - if I would have had it I would have proved or disproved my hypothesis in less time than it took to write the first post). The testing required to validate the hypothesis has been explained (twice). The time for talking is over (except to exchange new hypothesis).

The point is: to hypothesize and test. This is the way to an answer. If one is really good one hits the right hypothesis first time every time (actually substitute God for good). There are a limit to the realistic possibilities but working without a basis can creat new ones.
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Last edited by stevebfl; 05-25-2002 at 10:38 AM.
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  #12  
Old 05-25-2002, 12:43 PM
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Stevebfl -- I'm sorry that I'm not following 100%. I've only had my Benz for 6 months and I am learning as quickly as possible. I hope you aren't frustrated with my inquiries. It seems that you are, or you are implying that I am not listening. Realize, you know this stuff like the back of your hand -- that is the very reason WHY I am asking....I don't know it.

Now, I do believe I follow on this: Somehow, I have the power seat diode that is failing, and therefore allowing current to flow the wrong way. (are you speaking of diagram 138/3? I found the diode in the power seat diagram on the 15R circuit). Problem is, I can find it on the diagram but that does not mean I can find it and fix it on the car.

I haven't found anything on the car, or in the diagrams, that refers to diode V1. You state that the diode "will connect fuse #9 which is hot all the time to fuse 2 which is connected to fuse 1 and that should only be hot with the key on. " Is this apparent when looking at the 9, 2 and 1 fuses from the top? Surely not, I see nothing. From reading savagetom's comments it appears that I must find it somewhere under the fusebox. If I will find more than one, which one am I looking for?

If you can give me directions as to how to find it, remove it, and test it, I would surely appreciate it.

Sorry to be so hardheaded on this issue (however, if you want to discuss the standard deviation vs. benchmark, considering beta, alpha and sharpe ratios on open-ended mutual funds -- I'm your man. Everyone has their field of expertise -- this wiring is not mine.),

Thanks,

brookspw (yes I have the CD)
__________________
1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles

Last edited by brookspw; 05-25-2002 at 01:35 PM.
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  #13  
Old 05-25-2002, 01:52 PM
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I am not at the diagrams so I will have to wing it. First if you have found the drawing for the power seats and the diode, this is what you need to find. The first pages of the ETM (electrical troubleshooting manual) would show the layout of the fuse box.

The fuses are under a cover that easily comes off. There is a further cover which comes off with a number of screws. this exposes a number of relays. Find this illustration in your CD. The diode is the only device of its kind in the section that has multiple relays all plug in with multiple pins except the diode. It is at the exact left rear corner and has only two pins. Pull it out and see if the symptom (radio plays with key off) still exists. If it doesn't make any difference then we need to think up another hypothisis, probably based on a little further checking.

As to tracing the circuit. Go to the drawing that has the diode V1 (power seat drawing of source power - more than one page of power seats). You will notce that fuse #9 is sourced at term 30. That means it is hot all the time. Connected through the door switch and then the diode wiring is fuse #2 which is only powered by circuit 15 (key on). If the diode is shorted these two circuits become powered whenever the door is opened. Now find the drawing, also at the front of the book, which describes the power flow. It will show fuses and which cicuits they power. It will also show where they get their power and which are connected at the source power side. Fuse #2 is bussed to fuse #1 on the source side and fuse #1 is the switched power fuse for the radio.

But before any of that go out to the car and pull that darn diode and see if it kills the problem. I am dying of curiousity.
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  #14  
Old 05-26-2002, 02:02 PM
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Ok, I'll be pulling the cover (s?) off of the fusebox today to get to the diode.

Is the "cover" you mention the black plastic compartment that contains the top layer of fuses? (Is it under those fuses?)

I will report my findings.

brookspw
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1994 C280, dark green metallic
105k miles

1991 190E 2.6, Black
191,500 miles
(sold to another forum member)

2003 Chevy Tahoe LT, Redfire Metallic
105k miles

1989 Mustang GT Cobra Convertible
43k miles
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  #15  
Old 05-26-2002, 08:19 PM
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I don't know for sure but I think it is underneath the fusr box. I couldn't find on the top of the fuse box in my 87. I think you can access by removing the kick panel and reaching up from the driver's foot well. Good luck!
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