I couldnt get my W123 started after being stood for the winter, so I replaced the starter. Still no joy. I've tested all the wires out, and there's a hard-start relay in the circuit, but since I put a new starter in I'm not sure what cables should go where.

I have the IGN-ON line from the ignition switch (which works), and then three wires on the starter itself. One from the main solenoid "hot" bolt, one from the small solenoid switch and one small one on the starter itself.

Using the Bosch 30A relay, which wire goes to which pin number? (85, 86, 87 and 30?) I'm really confused and can't for the life of me work out why the car isn't starting.

gosh, without seeing the relay, I find it hard to help much. can you take a picture of your "hard start" relay? there should be two large terminals, and two small terminals... take a pic.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The relay in question is just a standard Bosch 30A one, like this:

Does the starter engage by jumping the first and last screws in the black box located on the passenger inner fender?

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I havent found this "little black box" that I've read so much about on this forum - my model is so basic that I don't think it was fitted.

Either way, at the moment all the cables to the starter are disconnected (since I replaced it) - I need to know how they reattatch.

I was having a problem like this just days ago.

I'm not sure about your car, but I'll post a link to a picture that helped me. Maybe it will help you figure out which wires go together at least, if anything.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/48676d1192356727-hand-held-starter-switch-cd-047.jpg

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1974 240d "Peace, Love and Empathy" - Kurt Cobain
1982 300sd "It all depends upon the Benz!" - Me
1983 300sd
1985 500sel
1992 300se

what colors are the wires??

I'm going to think about this considering my little black box and the basic flow going on inside the relay...

the two BIG red wires going to the solenoid are supposed to have connection to the fat white wire at all times. (85 & 86 on relay).

to switch the starter on/off, all of them need to come in contact with the smaller white wire (the smaller stud coming off the solenoid). When they do, the starter turns, when they're not, the starter is off. Just like how you would connect a remote starter on a car with the distribution box. All the remote starter does is close the circuit between the 3 sets of wires (2 are already closed, but 1 is brought into the circuit, just like 87a is closed, bringing the wire into the circuit and 87 is not, opening it, in the relay).

To put this together, your picture of the relay means that on 87a & 87, the smaller wire needs to go there. And on 30, the "white" fat wire goes there (if there is a fat white wire)....and then finally on the other two, there should be 2 red wires. I'm not sure if it matters which one goes where, but one goes on 85, one on 86.

NOW, if you DO NOT have 2 red wires and 2 white wires, as I've said there are, please don't do anything and post up what color wires you have and the diameter of each one. (fat...skinny...if there are only 2 sizes, that's all you need to say). I do not believe there is a ground.

I believe this would be the same as the connections in the little black box would be (if they went to a relay instead).

If anyone thinks I am not right in my translation of the black box to the way the relay would be wired, speak up!

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1974 240d "Peace, Love and Empathy" - Kurt Cobain
1982 300sd "It all depends upon the Benz!" - Me
1983 300sd
1985 500sel
1992 300se

As I said, I don't have the black box. I don't really have any of those coloured wires either, but I appreciate the help.

Basically, the starter needs a live, a ground and a switch, correct? I know how to wire the relay to provide them, but I don't know the connections on the actual physical starter itself.

Thanks for pulling that up! It's my SD, was not able to re-attach.
The 123's have a similar box, but with three screws, use the first and third. The first pic is a "close up", the second is a wider shot to help locate, just in front of battery.

Attached Thumbnails

   

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Please, you guys really aren't reading what Im saying.

1) I don't have the little black box.
2) I have some cables flopping around my engine bay.
3) I have a starter with no cables attatched to it.

Which cables go where on the starter itself?

Ok, I worked it out. For future reference:

The TWO large cables (one from alternator, one from battery +) go to the top solenoid post.

One small cable also from large solenoid bolt to relay point 30.
One small cable from solenoid switch to relay point 87.
One small cable from small starter screw to relay point 86 (acts as ground)
One small cable from starter to relay point 85.

This way, when you turn the switch, it sends 12V through the relay, closing the main relay poles between the solenoid and its switch.

And it works! The car turned over for the first time in 18months! I just need to trickle-charge the battery now to get her fired up (the weedy 60A alternator on my Audi wouldn't jumpstart the beefy 90A battery that's in the Merc!)

Case closed! Thanks to all those who chipped in!

sorry for the lack of help I would've told you that if I read it
I just rebuilt my starter 3-4months ago I didn't have the the black box either
81 300D I grew up in Bydgoszcz Poland

hahah, masz beczka tez? Moje jest moj pierwsze samochod w Polsce - jestem Anglikiem

You have a very tidy engine compartment, nice too see.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Thanks!

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