'73 280 won't stay running - Mercedes-Benz Forum

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post #1 of 18 (permalink) Old 04-07-2009, 09:38 PM Thread Starter
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'73 280 won't stay running

Hello all,
I am restoring a 1973 280 and started it for the first time today. The PO mentioned that the car wouldn't stay running once the key was released after starting. I passed it off as craziness, apparently I shouldn't have! What happens is this....I turn the key to the crank position, the car starts and will run as long as the key is kept there. Once I let it go to the 'run' position the car instantly stops. Obviously I can't drive it like this and I don't want to wear out the starter. I really don't even know where to start on this one! Any help will be greatly appreciated!


Also the BRAKE and GENERATOR light stays on

Last edited by vinteretpoijka; 04-07-2009 at 10:14 PM. Reason: Added aditional information
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post #2 of 18 (permalink) Old 04-07-2009, 10:06 PM
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Best guess is that you may need a new ignition switch.

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #3 of 18 (permalink) Old 04-08-2009, 05:24 AM
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Easy to check, put the ignition on and see if you have power at the positive side of the coil.

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post #4 of 18 (permalink) Old 04-08-2009, 06:22 PM
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Popuptoaster is right. Maybe a bad ceramic ballast resistor??
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post #5 of 18 (permalink) Old 04-09-2009, 10:14 PM Thread Starter
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Checked the coil and I have power at the coil with the key in the run position. Should I check the ballast resistor next?
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post #6 of 18 (permalink) Old 04-10-2009, 11:02 AM
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IMO, yes. You can use an ohmmeter, or just jump from the Pos. battery terminal directly to the coil. See if it starts and stays running. If it does, it's probably the resistor or at least something in the "run" wiring circuit. Don't continue to run the car with this jumper though, as it may eventually burn out the coil. Aren't cars fun??
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post #7 of 18 (permalink) Old 04-11-2009, 05:14 PM Thread Starter
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I replaced one of the ballast resistors, yes ONE of them. For some reason there is two of them. One of them has one red wire going to it which connects to the coil. The other has two red wires on one side and another two on the other side. I have no idea what these go to or what they are for. I tried starting the car again today and it did run for a short period of time then quit. Again it would run but very badly before quitting. I looked in the engine compartment and the new ballast resistor was smoking and the other was warm. Any thoughts?
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post #8 of 18 (permalink) Old 04-11-2009, 05:27 PM
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funnily enough mine had two in it although one wasn't connected, i think it may be just cos they are a bit awkward to get to to take outand easy to screw another one in.





Although you can't see it mines got two on both ends, not sure whats up with that, just from experiance on other types of car i would say one on one end will be power in from the ignition and on the other end one will go to power the coil and the other will come up from the starter motor to power the coil at a full 12v while cranking, on these Mercs i'm not so sure though, need someone with a bit more knowledge than i have i'm afraid.


To rule out the resistor i personally would run a live from the battery direct to the coil and see if she'll stay running then, dont leave it running to long that way though as the coil wont like a full 12v for two long, if its running just as bad, it cant be the resistor as you'll have bypassed that part.

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post #9 of 18 (permalink) Old 04-13-2009, 05:53 PM
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A couple comments, recommendations and questions, for what it's worth.

If your ballast resistor is smoking there is probably a short. There's no way should this happen, as it is there to reduce the voltage to the coil when in the run position. It's as though it is connected directly to ground. Has anyone messed with the underhood wiring? I am assuming you just purchased this vehicle, and if so, there is no telling what has been done prior to your taking possession. Does it look like obvious changes or modifications have been made? Perhaps (let's hope) some of the wiring has just been hooked up incorrectly.

If it were me, I would not start replacing parts unless I was relatively certain that the currently installed part is defective. This can get very expensive and may still not resolve the problem(s). The exception might be if you're planning to completely renew most underhood components. As an example, I am currently doing this with my '73 280C. I am replacing all hoses, belts, spark plugs, spark plug wires, points, condenser, cap, rotor, rebuilding heater control valve, power steering pump, rebuild carburator, radiator rebuild, etc. I've had my vehicle for 23 years now, and many of these things have not been touched in years, if at all, so I feel it's time to do it all.

You indicated that your vehicle ran for a short period after replacing the resistor. How did it run? Did it idle, was there good throttle response, could you put it in gear and it stay running, and when it finally quit, how did it quit....abruptly (like turning off the key), wind down (like fuel starvaiton, etc.? Have you tried to jump directly from the battery to the coil? If so, what happened then?

If you recently purchased this MB, has it started, idled, accelerated, and driven down the street for you at all? If not, I would recommend that you start at square one and troubleshoot and analyze each mechanical/electrical system to determine how many, if any, different problems you are dealing with. Then I would concentrate on each problem system and resolve it before moving on to another system.

These (older MB's) are pretty basic automobiles, and as such, relatively easy (compared to the new computerized vehicles) to troubleshoot and work on. At this point, (no offense meant) I would like to ask you to assess your knowledge of mechanical, electrical, and troubleshooting capabilities, and let us know what you feel they would be? The reason I ask is so that any of us who respond will know, approximately, how in depth to detail steps, procedures and actions you should take.

You indicated in your initial post that this is a '73 280. This would probably make it a 114.060, four door sedan, with a 110.921, in-line dual overhead cam carburated six cylinder engine. Is this all correct?

Finally, don't get frustrated. Gettinig it all going may take some time, but hopefully not much money. Keep us posted.

Last edited by mbbuff; 04-13-2009 at 05:56 PM.
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post #10 of 18 (permalink) Old 04-13-2009, 10:05 PM Thread Starter
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Thank you for all your help and your suggestions! To be quite honest I am new to Mercedes Benz. This is the first I've owned and first I've worked on. I currently own 3 BMW's and have owned several others. The oldest one of these vehicles is a 1992, one of them is a V12 750il. I'm not bragging but rather stating that I have no trouble working on any of them but this '73 280 is throwing me for a loop. On any of my BMW's virtually everything is electronic, there are diagnostic tests to determine problems, voltage, ohm tests etc. Points, condensers, ballast resistors are new concepts to me. You can bet that I will utilize this board a great deal.

As far as the immediate problem with the 280. It was hard to start. I had to remove the fuel tank, clean it, replace what seems like miles of fuel line. When the car finally started it ran rough then the idle smoothed out. I have the vehicle on jack stands so I did not attempt to place the tranny in any gear. When it quit it quite as if the key was shut off. After that I could start the car but only by pouring gas in the carbs. It would run for a few seconds, long enough to burn the poured gas a take a little from the carbs themselves, then quit. It was after doing this a few times that I noticed the resistor smoking. I'm sure things have been replaced and tampered with. To what extent I am not sure. I have included some pictures of the two resistors on the vehicle, maybe someone here can tell me if they are correct or not.

Again, any help will be greatly appreciated!!
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