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  #1  
Old 09-10-2013, 01:13 AM
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Grounding issue, BWDIK?

This is for my 1979 240D W123


After a week of misdiagnosis documented in this thread:

Ignition or tumbler or switch or ???

I think it is a grounding problem.

For the fun of it, I replaced the #5 fuse, disconnected then reconnected the battery.

Result:

All lights that are supposed to go on are on (dash, glow, dome, etc).

After the glow plug light goes off, I turn to crank, then nothing - everything goes dead.

No lights, no ticking sound of the clock, etc.


When I went to disconnect the battery, I hear a faint humming, electrical
like sound, like maybe from the cd player? But I can't tell for sure, since I am under the hood.
Because I was touching the battery connecting the terminal, I fulfilled the ground function?

What say ye W123 gurus?

And be easy on me, I'm just a girl...

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  #2  
Old 09-10-2013, 02:45 AM
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I think something is short circuiting.....what is on fuse number 5?

Now if you leave fuse 5 out, disconnect the battery.....reconnect with fuse 5 out.....does everything work or not?

How's the glow plug system? Does this have the relay on the firewall under the hood or dash? Loop plugs or pencil? Any modifications on the glow system?
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Old 09-10-2013, 03:14 AM
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I looked through your other threads....just by all the problems you've mentioned.....I really want to lay my cards on it being the ignition switch.....it seems like you were able to baby it along by wiggling the key...disconnecting the battery and other tricks...but it seems that it was slowly dyeing like in the case with a bad starter.....you can beat on it for awhile and jump of at the terminals to get it to go for a wee bit longer....but soon it will die....

If you remove the instrument cluster, you will see the switch right behind the ignition....you can unplug it and see if the pins are free of corrosion....you can also buy electrical cleaner and spray into he switch.....its possible cleaning it may revive it....or at least verify my guess....if it magically works again, then we know...
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Old 09-10-2013, 03:41 AM
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Pull the plug off of the back of the tumbler - work out which wire is which and just use a wire / wires to jump across the terminals to simulate the operation of the ignition tumbler.
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  #5  
Old 09-10-2013, 08:38 AM
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If the dome light and clock go off when you turn the key to start, then you probably don't have an ign switch problem. They don't get their power through the switch. I would guess a bad connection at the battery, battery to chassis ground problem, battery to fuse block open, or something like that. A simple 12V test light is the best test equipment for a problem like this. Use a test light with an actual bulb, not a LED. You can use a DVM here also, but a test light is actually better in this case.
Using the test light, make sure you have ground where you should have ground and power where you should have power. Keep an eye on the dome light because if it comes back on, then the problem has gone away as far as testing goes.

Paul
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Old 09-10-2013, 09:19 AM
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When a Starter is not working My preference is to clip on a remote Starter Switch (bypassing your Starting Circuit) and see if it works with that.

If it works all the time like that you know you have a Electrical Circuit in the Starting System issue.

If it does not work reliably with the Remote Starter Switch connected and your Grounds and Cable connections are good it is likely the Starter or some component on the Starter.
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  #7  
Old 09-10-2013, 10:20 AM
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My vote is the Ground Strap between the body and chassis. Remove it and clean the connections. This gave me fits one time.

Charlie
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Old 09-10-2013, 11:36 AM
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Quote:
Originally Posted by pmckechnie View Post
If the dome light and clock go off when you turn the key to start, then you probably don't have an ign switch problem. They don't get their power through the switch. I would guess a bad connection at the battery, battery to chassis ground problem, battery to fuse block open, or something like that. A simple 12V test light is the best test equipment for a problem like this. Use a test light with an actual bulb, not a LED. You can use a DVM here also, but a test light is actually better in this case.
Using the test light, make sure you have ground where you should have ground and power where you should have power. Keep an eye on the dome light because if it comes back on, then the problem has gone away as far as testing goes.

Paul
Is a DVM a digital volt multi-meter or ???
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  #9  
Old 09-10-2013, 11:40 AM
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Quote:
Originally Posted by cooljjay View Post
I think something is short circuiting.....what is on fuse number 5?

Now if you leave fuse 5 out, disconnect the battery.....reconnect with fuse 5 out.....does everything work or not?

How's the glow plug system? Does this have the relay on the firewall under the hood or dash? Loop plugs or pencil? Any modifications on the glow system?
The reason I replaced #5 was because another thread had mentioned it, and it was easy, so I did. #5 related to AC, which I don't have, and I forgot the rest - didn't seem like it applied like the AC.

Yeah, will try taking it out as you mention, for an easy test.
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Old 09-10-2013, 11:53 AM
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Quote:
Originally Posted by cooljjay View Post
I think something is short circuiting.....what is on fuse number 5?

Now if you leave fuse 5 out, disconnect the battery.....reconnect with fuse 5 out.....does everything work or not?

How's the glow plug system? Does this have the relay on the firewall under the hood or dash? Loop plugs or pencil? Any modifications on the glow system?
Yes, it sounds like a short circuit problem.

The glow plug system was recently changed (by me, applause!) to the pencil style with parallel wiring. Made sure the ground wire at the end by GP #4 was disconnected.

(This was about 3 months ago, ran great until I had a vacuum diaphragm tear, that I replaced about a month ago - done again, by me and this great forum, of course )

I have a spare relay (mine is located under the steering wheel), that I can switch to test.

Now that I think about it, when I disconnected the relay before, the harness got all messed up (couldn't positively determine if the wires in the harness
were in the original order). I asked for a diagram or picture and someone had a photo, but the colors of the wires were different.
I should re-visit this, with a diagram with numbers.

Last edited by mbzr4ever; 09-10-2013 at 12:06 PM.
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  #11  
Old 09-10-2013, 03:21 PM
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Quote:
Originally Posted by mbzr4ever View Post
Yes, it sounds like a short circuit problem.

The glow plug system was recently changed (by me, applause!) to the pencil style with parallel wiring. Made sure the ground wire at the end by GP #4 was disconnected.

(This was about 3 months ago, ran great until I had a vacuum diaphragm tear, that I replaced about a month ago - done again, by me and this great forum, of course )

I have a spare relay (mine is located under the steering wheel), that I can switch to test.

Now that I think about it, when I disconnected the relay before, the harness got all messed up (couldn't positively determine if the wires in the harness
were in the original order). I asked for a diagram or picture and someone had a photo, but the colors of the wires were different.
I should re-visit this, with a diagram with numbers.
I posted that photo for you....here's a link to the electrical wiring diagrams...on page 20 is the glow plug timer and you will see the pin number and the color for the wire....

24 Electrical Troubleshooting

Have you pulled fuse 2? And inspected it? The dome light, instrument cluster, ignition switch all run off this fuse and these are what you are having issues with.....

If you haven't done so yet, all your fuses should be replaced with copper/brass and ceramic fuses....the original aluminum fuses corrode where they contact the copper tabs in the fuse box....causing issues...
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Old 09-12-2013, 01:59 AM
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Quote:
Originally Posted by cooljjay View Post
I think something is short circuiting.....what is on fuse number 5?

Now if you leave fuse 5 out, disconnect the battery.....reconnect with fuse 5 out.....does everything work or not?

How's the glow plug system? Does this have the relay on the firewall under the hood or dash? Loop plugs or pencil? Any modifications on the glow system?
Number 5 fuse: Air conditioner compressor (I have no AC)
Switch over valve idle stabilization

Number 12 fuse: Instrument panel, and some other stuff
I put in a new fuse here.

Took the #5 out, key in, turned to where all the lights on dash + glow plug go on. When glow plug goes out, turned again to crank, but nothing.
Everything dies, all lights, including dome light.
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  #13  
Old 09-12-2013, 02:01 AM
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Quote:
Originally Posted by charmalu View Post
My vote is the Ground Strap between the body and chassis. Remove it and clean the connections. This gave me fits one time.

Charlie
I don't know where this is.

Do you mean the ground strap between the battery and the chassis?
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  #14  
Old 09-12-2013, 02:20 AM
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The ground strap is under the drivers side of the car running from the body to the transmission....I was just poking at mine today....

That's a very strange problem, that when the car is rest...the lights come on but them when you try to engage the starter....everything dies....it possible its the ground strip....but I just don't think so....

Does this model have the terminal box near the battery, with three screws in it?
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  #15  
Old 09-15-2013, 02:09 AM
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Quote:
Originally Posted by cooljjay View Post
The ground strap is under the drivers side of the car running from the body to the transmission....I was just poking at mine today....

Does this model have the terminal box near the battery, with three screws in it?
I found the ground strap totally black and oiled up from over 30 years of use.

I managed to disconnect the side to the chassis, but the connection to the tranny puzzles me.

How does one loosen the nut - is it from the other side?

And is it worth cleaning, or should I just go about ordering a new one?

No, there is no terminal box with 3 screws.


Last edited by mbzr4ever; 09-15-2013 at 02:27 AM.
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