Electrical Issues beyond Me

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bavbob

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I have already posted that I have a 73 euro (6/28/73) 3.0 Cs with no power to the back windows ( fronts are manual) or sunroof. The car will run and the dash lights all work as well as the instruments. I have read thru countless posts on electrical issues. I believe my load shedding relay is working and there is power across the fuses. As usual, there has been a bunch of aftermarket alterations. I present images below of what I have: I believe the fuse box setup to be incorrect, the relays ok. ....I am totally lost and have spent 5 hours upside down with no insight.

Fuse Box Rear from #10(bottom) to top
fuses 10 to.JPG



Relays under dash, believe the one with the black relay to be the Load shedding relay, other a window relay.
IMG_0876.JPG



There is another relay besides the signal relay, way back in the dash

relay farthest back.JPG



and the wiring to the door switch and what I believe to be dead wiring for a potential front door power window set up.

Discon front window.JPG


There was also this junction of 3 sets of brown wires joined to the body of the car/common ground. I bypassed the current ground for another due to rust and poor contact. Interestingly, one of these already contains a ground cause when I join the 3 alone, the black relay in the image above clicks.

IMG_0882.JPG
 

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bavbob said:
I have already posted that I have a 73 euro (6/28/73) 3.0 Cs with no power to the back windows ( fronts are manual) or sunroof. The car will run and the dash lights all work as well as the instruments. I have read thru countless posts on electrical issues. I believe my load shedding relay is working and there is power across the fuses. As usual, there has been a bunch of aftermarket alterations. I present images below of what I have: I believe the fuse box setup to be incorrect, the relays ok. ....I am totally lost and have spent 5 hours upside down with no insight.

Fuse Box Rear from #10(bottom) to top
View attachment 87761


Relays under dash, believe the one with the black relay to be the Load shedding relay, other a window relay.
View attachment 87763


There is another relay besides the signal relay, way back in the dash

View attachment 87764


and the wiring to the door switch and what I believe to be dead wiring for a potential front door power window set up.

View attachment 87765

There was also this junction of 3 sets of brown wires joined to the body of the car/common ground. I bypassed the current ground for another due to rust and poor contact. Interestingly, one of these already contains a ground cause when I join the 3 alone, the black relay in the image above clicks.

View attachment 87767
Click to expand...

do you have or need the electric drawings and instructions ?

my guess is that despite you have been very precise telling us details about your car, thank you, it will be very difficult to help you out with this

if you need drawings do ask me, i will check
 
My electrical teachers taught me to troubleshoot things from the end backwards, whether it is an audio amplifier or an electric window.

So here are the steps:

1) Pick a rear window, look at the motor. There are two variants: a) three inputs: ground, +12V UP, + 12V Down. b) two inputs: ground and +12V, reversible. The switches are naturally different. For a) the ground comes directly to the motor and the switch steers +12V to one or the other terminal, or to none.
For b) the switch provides both +12V and ground one way or the opposite way, or none.

For a) test that you have Ground using the ohmeter. Trace back where each +12V terminal at the motor comes from via continuity testing of terminal to switch.
This assumes that there is no window motor relay, which was the case for case a) from the factory. If there is no such continuity then the wire harness has to be examined.
I have not opened the rears but I assume it is trivial as it does not go through doors...
Always useful to briefly run a +12V to one and the other terminal straight from the battery to ensure the motor moves in both directions, and that the glass follows...

For b) again continuity test both motor terminal to the switch (with contact OFF or battery disconnected). The ground is easy, with the switch activated there HAS to be continuity to ground in one of the two terminals. In the other activation there HAS to be continuity to ground in the other terminal. If this fails, explore the wire harness.

2) Once the motor to switch path is understood, there are three options: a) the ground circuit is failing, b) the +12 circuit is failing. c) both.
Ground should be the easiest, either find where it was supposed to be grounded and fix contact/wire that needs fixing or just create a new ground attach.
For +12 not reaching the switch now you can go back to fuses, load shedding relay, etc. Here is where DQ's suggestion of using wiring diagrams seems a must.

Watch out for Red Herrings:

3) Door switch - some late cars have a relay controlled way of powering the window motor with no contact while the door is open. But whether this circuit works or not
should have no effect on your troubleshooting. It may power the 12V with no contact, just be careful with that.

4) Overload fuse - some late cars have a fuse that pops on current overload. If you have one, there could be the problem, determine that and bypass if needed.

5) Some owners have added relays to the window motors. That changes everything. For front windows the relays are placed inside the door. For rear the relay can be anywhere as it is easy to add wires to the harness. The main difference in troubleshooting is that you shut the radio and listen for things that click instead of motors that move.

I bet 11 dollars (upping the ante SFDon...) that you have 1) b), 2) b), with fault at 4) and no relays.
I bet 13 dollars the Coronavirus is defeated by the one force stronger than a 0.1 micros virus on April 15th...The IRS.
 
Last edited:
I will address your recommendations in a few days when I can return to this task. So far

1) Motors are the newer ones, four spades, two on each side. There are 4 relays under the dash, one load shedding, one for the wipers and I assume the other two are for the windows.
2) I swapped out the relays and I have 12.5 V to the motor on both sides with window switch depressed, but no movement. Swapped around switches with no change. Ran a ground to the motor directly and still no go even though the blue wire shows 12.5V with switch depressed.
3) I rebuilt the motors but put 12V battery directly to each, all work fine, windows and sunroof.
4) Fuse 10 should have a green/blue wire for the sunroof, it is not there. The sunroof switch is new and it has a green/blue wire to it so not sure where the thing went to.
5) I found my heater blower motor line joined to fuse #8 and not #9 so swapped it and got that to work............something positive.
6) Both doors are gutted so no switches for the dome light, wires in the breeze. Have dead end wires that I believe to be for front motors which I do not have (see second to last image in original post).
7) I have only 2 grounds that I could find. Braided from tranny to firewall, braided from hood to radiator mount. Could not find any from PS fluid reservoir or alternator etc. I cleaned the ones I found. Also cleaned and remounted the wires in last image above to front driver fender from under the dash.
 
A late 73 should have two circuit breakers under dash, are they there and are they tripped? In a 73 the dome light driver side switch activates the relay for the window motors without ignition having to be on. I have a thread with pics of all uneed dash relays which I will find and post here. You can check the wire colors from the pics.

Relays Under the Dash

I have been trying to help Roger in New York sort out his wiring as he reassembles two coupes. The wiring diagrams are hard to read sometimes and if you have a 73 1/2 when window motors/switches/circuit breakers were added you have to use the early diagram as well as the 74 diagram. There are...
www.e9coupe.com www.e9coupe.com
 
bavbob said:
2) I swapped out the relays and I have 12.5 V to the motor on both sides with window switch depressed, but no movement. Swapped around switches with no change. Ran a ground to the motor directly and still no go even though the blue wire shows 12.5V with switch depressed.
Click to expand...

I assume you have 12.5V to one side with window switch depressed one way and to the other side with window switch depressed the other way, right?
Did you measure ground continuity from the other terminal with window switch depressed?
 
I so appreciate the input here, it relieves some frustration I have and am sure I will solve this issue with your help.

Chris: I had read your post and confirmed all the wiring to the relays. The "nest" of brown wires that are screwed into the front fender were all pulled and cleaned and replaced. I did notice that with the ignition on, one of the relays clicked on when touching all the brown wires together indicating that one set of these was already grounded, at least that is how I interpret it. Also, I have the door dome light switches out and the wires hanging in the breeze. I did confirm that I was getting voltage to the dome light wire though the light is not installed.

Arde: I have 12.5 volts to the blue wire to the window motor when the switch is depressed in one direction , I did not check to see if the voltage switched to the other wire when depressed in the other direction but will this evening.

How to test ground continuity: If the ground is within the switch, not sure how to test for continuity. Can I test by engaging the switch in one direction and while doing so, check resistance from the other motor terminal to the chassis? I plan to take a multi-meter and check resistance , not sure what value would be acceptable.

I have zero power to the sunroof. Again, there is no green/blue wire from fuse 10. In my original post, the first image shows what I had at fuse 10. You can see the green/brown wire on 10 when in fact , that should be on 8. Hence at fuse 10 I now have two violet wires only. I plan to run a wire from 10 directly to the sunroof switch at the terminal that has a green/blue wire.

Is the green/blue wire in my first pic at #9 supposed to have a piggyback to #10? I recall a picture, perhaps by Markos of the back of the fuse box and there was a green wire piggy back setup.
 
Yes, that works. I would do that with the battery disconnected to protect the ohmmeter in case you hit the other one.
The expected result is less than 0.5 ohms for one terminal and the motor winding resistance (say 10s of ohms) for the other.
If you disconnect the terminals from the motor it should be less than 0.5 for one and infinite for the other.

Then repeat for the other activation of the switch and the result should be the reverse.

Aren't manual windows great?


bavbob said:
How to test ground continuity: If the ground is within the switch, not sure how to test for continuity. Can I test by engaging the switch in one direction and while doing so, check resistance from the other motor terminal to the chassis? I plan to take a multi-meter and check resistance , not sure what value would be acceptable.
Click to expand...
 
With ignition on, hearing the click when grounding the brown wires is good, it indicates that one of the relays is working. You should get the same response when grounding the second ground wire at the drivers A pillar. Ground this wire again with ignition off, not the dome light wire.
 
Thanks for this, I thought it was to #10. Did this fuse box come from a car with an electric sunroof? I think the purple wire at 10 is for the ignition but where is the input across #10?
 
bavbob said:
Thanks for this, I thought it was to #10. Did this fuse box come from a car with an electric sunroof? I think the purple wire at 10 is for the ignition but where is the input across #10?
Click to expand...

Unfortunately I couldn’t say. It’s not from my parts car. Other than triaging a few issues and stripping out all of the extras, I haven’t concerned myself with wiring. My 2800 is as spartan as you can get, so the wiring is beautifully simple.
 
Bbob: As you've stated above, there is power to the window motors, and the motors have been proven to work, and the motors have grounds when in place, then the only remaining issue is that your window regulator mechanism is stuck.

To test: when you press the switch is there a faint "clunk" at the motor? This would be the motor taking up slack in the transmission and to the window gear.

If no clunk, it's still possible your regulator is stuck and this was a common issue discussed years ago. The regulator runs until the little rubber baby buggy bumper, for lack of a more accurate term, comes up against the stop on the regulator mechanism. You know this... It runs full speed (the only one it has), so when it stops, the whole gear train is under load when it comes to the stop. Like parking a car with AT on a hill when you may have to jack up at least one rear wheel to take the load off the drivetrain. There may be enough friction in the regulator, together with the strain of the sudden stop, that the motor can't unwind the regulator. IIRC it may be more common in the fully closed position, which of course would be preferable to a window that doesn't close.

To get at this you'll have to unwind the window using a finger or the little toothed nylon strip that should have come with the car. These are scarce now, I think, partly because no one figured out what they were for unless the RTFM at an early age. Unwinding by finger is a little tough on the finger (AMHIK) and the gear reduction is such that it takes forever and a day to get appreciable motion from the glass. The good news is that you only have to unwind the regulator enough to take the strain off. After that, the window "should" work.

HTH
 
HTH many thanks. I rebuilt everything as this is a restoration so all parts have been cleaned and re-greased and application of direct power shows the windows go up and down nice and quick. It is the sunroof that I am also dealing with as no power is getting to it. I had to use porsch parts to rebuild it so willl not put on the new header until I know the thing works.
 
Eureka!. The PO abandoned the sunroof for the aftermarket VDO gauges he used. I found the line to the sunroof tied up buried under the dash. I think he did this because the cables were fused into the guide tubes. I swapped all that out. I re-established the connections and it works perfectly now!. Windows I will tackle tomorrow.
 
Do I feel dumb or duped. Turns out all 4 switches were out. Even though they were switching power to the motors, the ground was not functional. Took em apart, cleaned them and all is well. BTW: One bezel was shot so I ordered Mercedes part 001821515 , $42 rather than $80.
 
Great news.
I do not buy that all four switches would not switch ground, more likely they did not get ground, and in the process of removing/cleaning the ground path was restored :)
it is the "Four witches were switching four switches, which witches were switching which switches?" argument.

bavbob said:
Do I feel dumb or duped. Turns out all 4 switches were out. Even though they were switching power to the motors, the ground was not functional. Took em apart, cleaned them and all is well. BTW: One bezel was shot so I ordered Mercedes part 001821515 , $42 rather than $80.
Click to expand...
 
bavbob said:
Thanks for this, I thought it was to #10. Did this fuse box come from a car with an electric sunroof? I think the purple wire at 10 is for the ignition but where is the input across #10?
Click to expand...

I know this is unrelated to your specific issue, but since this picture has arisen yet again (Thanks Markos), and I have spent hours staring at it, I can answer this question. Fuse number 10 on this fuse block is for the radio circuit.
 
I believe the older switches have their own ground. I had only been dealing with two for each back window. I took the two from the center console and tried those, one worked for a second and the discovery went from there. Other clue was switch would measure 12.3 volts in one direction but only 4 volts in the other.
 
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