Did I kill my starter? 1970 250c w114 - Page 3 - Mercedes-Benz Forum

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post #21 of 34 (permalink) Old 12-24-2014, 04:20 PM
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Have you tried using a remote start?
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post #22 of 34 (permalink) Old 12-26-2014, 11:05 AM Thread Starter
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I have not tried a remote start.

I just now realized that the positive lead on the starter always has 12v on it, and the neutral safety switch and ignition switch only control the ground connection to the starter solenoid.

The casing of the starter is grounded. So I need to get my clips on the contacts to starter solenoid now.

http://youtu.be/8WD5Q_PF3pM

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post #23 of 34 (permalink) Old 12-26-2014, 11:52 AM Thread Starter
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So there are three wires that go to the starter:
1) one big always hot wire. There is a similarly large wire that goes from a similar connection on the starter solenoid to the starter casing. I have to guess that this is a high amp ground wire for when it's actually cranking. I don't know, but it's part of the starter assembly and I assume it doesn't matter. You can see those wire in the picture of my spare starter below.
Did I kill my starter? 1970 250c w114-imageuploadedbyautoguide1419619780.659688.jpg

There are also two small wires on the starter solenoid.

2) in my blue coupe, the bottom wire is constant ground.

3) the second small wire that is higher up seems to get about 10v when I turn the key to the ACC position and doesn't change when I turn the key to the start position.

I guess I will have to test these on my other w114 car to see what it's supposed to do in each position.

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post #24 of 34 (permalink) Old 12-26-2014, 12:08 PM Thread Starter
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Ok. Checked the connection I call "3" in the above, actually labeled "15a" on the (slightly different) parts starter I have. (The one I call "2" above is labeled "50".) and it seems that the behavior is the same with the exception of what happens when I turn the key to the start position. The volts go full-hot and match that of the battery. (I was taking all my voltage measurements against the battery positive, and the volts went from 13 to 3 to zero.)

So it seems everyone is correct and that there's something fried in my neutral safety or ignition switch.

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post #25 of 34 (permalink) Old 12-26-2014, 01:39 PM Thread Starter
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The last thing I tried to do was "jumper" the hot contact and the "15a" contact while under the car, just using jumper cables. It wasn't a safe maneuver, so when nothing happened, I gave up assuming that the corroded metals weren't making good contact. That's when I noticed the robber boot for the hot wire had been pulled back before I ever started messing with the car. I'm guessing that someone else had started down this road with this car.

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post #26 of 34 (permalink) Old 12-27-2014, 07:29 AM
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Having constant 12V (battery voltage) is correct for the "key on/run" position on your car.

The other small terminal engages the starter solenoid.

As suggested, use a remote starter switch to supply 12V to this terminal. If the starter engages then start looking into the wiring system.

Having a good ground/earth connection is CRUCIAL to proper operation of the start/charge circuits.

Check all grounding strap areas (battery to fender, starter to frame, etc.) to ensure you have a good clean connection.

It's not unusual for a well meaning mechanic to leave off a grounding strap because he figured, "It's JUST a ground strap, there's two or three other ones".

European cars use voltage relays as opposed to early American Iron which simply used fuses to supply voltage.
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post #27 of 34 (permalink) Old 12-27-2014, 11:58 AM Thread Starter
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The plan (today?) is to get a remote start device. It will be helpful to have around. I think I want to be able to bolt it on as the stew contacts are a little corroded, and I got no action when I touched my jumper cable end on both the hot bolt and the one that is supposed to get 12v in the start position.

Someone told me to check fuse #2 which is for the radio (strange), but I found no problems or difference there.

If there are any wiring problems like the neutral safety or ignition switch, they won't be getting fixed, as I'm planning to part this one out anyway. It would just be nice to get it mobile and postpone the inevitable.

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post #28 of 34 (permalink) Old 12-27-2014, 10:04 PM Thread Starter
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Didn't get the remote starter button today, but I did crawl under and:

1) verify the starter spins when jumping the two large bolts on the solenoid, providing power to the starter without engaging the bendix

2) try to jumper the solenoid power to only hear a click

3) determine that one of the small ground wires appeared really cooked with very brittle cooked insulation. Touching the wire, I broke it. So I believe that I may have fried either this ground wire or the solenoid, or both.

I think I should just proceed with my part out, and forget about it. It's been a good learning experience .

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post #29 of 34 (permalink) Old 01-13-2015, 10:15 PM Thread Starter
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Did I kill my starter? 1970 250c w114

Since I am neither have the space, nor the time right now for a part out, I thought I would try just one more time with my diagnosis.

(What was that wire that I fried from the "50" connection that seems to always be ground voltage? And why was it always ground voltage?)

I bought a remote start button, and want to know what to connect it to, and why the "15a" voltage is about 3v lower when not in the starting position.

I read up a little, and now see the volts correlate to the coil voltage and are probably 3v lower than the battery due to the in line resistor for the transistorized ignition. Ahh... Ok.

So what's the "50" connection, and why is it always ground? Oh... Is this just an extra/smaller bolt for the smaller wires that get extra voltage during the cranking? I remember from diagnosing the ignition on the white sedan 1971 250 that one ignition resistor is bypassed during cranking. So... Is "50" just the same thing as the power to the starter? And if my solenoid was firing/working, it would go to the 12-13v that the battery has??? Hmm...

Bosch Terminal Numbering Defined:
http://www.type2.com/library/identifi/bosterm.htm

And ignition wiring diagrams in posts 69 and 71:
http://www.benzworld.org/forums/8027346-post.html

Ok. So anyway, I should put the remote starter wires on "15a" and the battery hot. If my solenoid doesn't pop and provide current to the starter, then I know the starter solenoid is bad, and I might want to just replace it.

That's where I am. It's 21 F outside right now. So maybe tomorrow.

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Last edited by Fonzi; 01-13-2015 at 10:29 PM.
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post #30 of 34 (permalink) Old 01-14-2015, 05:25 PM Thread Starter
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Did I kill my starter? 1970 250c w114

RESOLUTION:
----------------------------
Did I kill my starter? No.

Melted the wiring or other starting position item. Most likely that wire that crumbled in my hand connected to "50", the lower small starter contact.
----------------------------

Solenoid sounded like it fired when I used remote starter to jumper battery hot (large top contact on starter) to the top small contact, "15a". I thought maybe solenoid was fried or jammed.

I figured I had nothing to lose by connecting to the bottom small contact "50" instead of the "15a", and what do you know. The starter fired. I'm back to where I was before but with no start-from-key. I guess that wire that was all cooked up on the "50" contact must have been important.

http://youtu.be/DrNA0s6lEZ8

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Last edited by Fonzi; 01-15-2015 at 07:41 AM.
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