1979 350se w116 - Just wrapped up a project with the alternator (new alternator and harness plug), WUR, fuel pump assembly... a new issue came up. Basically sometimes when I try to start the car, the starter seems to just run out of control. It is not grinding but just running, and when I remove the key it just keeps going. The only way to stop it is to unplug the battery. Never had this issue prior to finishing the other project. Any ideas?

Always go back to the last thing you did. I'd unplug the alternator harness and see if the problem continues as a first step.

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HMMM, the problem with the harness was that the plug had shorted out and fried. So i am wondering if this starter issue caused or had something todo with the alt plug. hmmm. I have no idea exactly how long the plug was like that, I must have been driving the car for at least two weeks before i figured out there was a problem. and all during that time there was no issue with the starter until after the new alt and plug was installed.

I dont think it could be anything else making that sound. basically i turn the key to start position and its like something didnt catch and the motor for the starter just keeps spinning, but again no grinding sound, during which the engine is not turning over.

The spinning without engaging is a typical solenoid issue, the solenoid is not moving the starter's gear into position.
I have never head of a starter going on it's own, except when two wires external to the starter touched, but I suppose it could be something internal in the starter.

Awesome, that sounds like what is going on, seems like something was not engaging. How does one. Can the solenoid be replaced separately from the starter? I saw a neighbor change a starter in his w123... if i have to change mine i hope it is easier lol he was not a happy camper. I suppose I should start by checking it to make sure the wiring it properly attached. seems some people recommend smacking it with a hammer a few times.

Sorry, I am not familiar with MB starters. On most starters the solenoid can be replaced separately.

Csaba

OK so I took a peak at the starter today and it didnt seem like there were any issues with the wiring. Im sure I can change it myself but given the potential for a short somewhere and potentially frying an alternator again i think i want to take it to a shop just to be safe. I got a quote from what seems to be a top shop here in town For $220 installed for the solenoid (if this is indeed the issue) and either $50(30min) or $90(1hr) for inspecting the electrical system. I think $300 seems reasonable. If i do this my self and there is still a problem and something else breaks it will end up being more expensive. Seems like a reasonable price?

Hmmm the thing that gets me is that is runs on after the key is out... could it be an issue with a relay?

OK So here is the latest... When the alternator is plugged in, I put the key in the ignition and the battery light is on. It seems to have the starting problem more often. When The alternator is not plugged in the battery light on the dash does not come on and it started 5 times in a row successfully. I am thinking I did not have this problem before because there was not a successful connection at the alternator because the plug was bad. It may not be the solenoid after all.

Allllright, A little more research. There is a rigged wire from the positive terminal of the battery into the relays (not sure which, i think it was the one on the right), it has a 30amp fuse as shown in picture. Needless to say this is clearly not a factory setup. The fuse was blown so i put a new one in. even with a new fuse the car was still having the starter issue. not sure what it hooks up too but i figured i would mention it. There is a loose end (shown in picture) coming out of the relay on the right, with no partner in sight. After seeing the car start fine without the alternator plugged in I am thinking it might be a problem elsewhere in the electrical system, so anything odd like this seems relevant.

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that fuse(30A) is most likely either starter or fuel pump and clearly doesnt belong but I'd leave it alone. Is this a K jet or D jet 116? looks kinda like an early one from the pictures, I'd assume your problem is either where the terminals meet (little plastic piece isolating each circuit usually on frame rail next to engine) or at the starter itself, if you melted the connecter at the alternator, odds are wires are melted either at the starter end, or maybe even inside the alternator/where the plug feeds. if not then maybe the ignition switch itself.

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R107.043 Euro 350SL (parts)(crushed)
W116.024 280se (crushed)
W114 280 (m110)
W108.067 280se 4.5
W108.068 280seL 4.5 (crushed)
W111 220SEB coupe
W110 200D went to the crusher
W110 190D sold sold sold

1970 Rover P6B

Used to own(1950 buick,1969 lincoln MK3,4G63t colt,87 300ZX, 79 F100, 92 XJ40)

Yea I am not sure what the 30a fuse goes to yet. I didnt want to take any chances with these odd electrical symptoms to I took it to "the shop". They say there is a short in the starter, which was my one of my initial thoughts, so a new starter is on the way, when i go there Monday I definitely want more info on this mystery fuse.