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 04:56 PM.