When I turn the key to start nothing happens with the engine. There is power to everything else and I checked the fuses (all good).
How do I know that the starter is bad? Could it be the solenoid? Or is just a break in the line?
I have been working this car for about a year and have done lot of work to get it really right. I'm very good at electrical work. I did rewire the ignition system and replace everything (coil, resisters, points, etc...). I have the service manual which helped a lot with that job. I'm just real sure how to go about this.
Any and all advise would be much appreciated.

Ok, first thing go under the car with a hammer and give the starter a few gentle taps. That will loosen the plunger in the solenoid if it's stuck. If it fires right away bad solenoid.

Otherwise unbolt it and bring it in to your local Autozone, pep boys .... and have them bench test it.

Another alternative, that I don't recommend, and I am not liable if you try this and run your sorry butt over is to disconnect the lead to the coil, put it in park, parking break, set the ignition to on then crawl under the car and jump the 2 leads off the solenoid. Sparks will fly so be warned...

Options one and two are best.

You can start getting a decent diagnosis when you tell us what we are working with..
If it is auto, then first suspect is NSS

Sorry about that MB 280SEL 1971.

Take a look at the Neutral Saftey Switch and cable under the hood...

Also, try "N"

There should be continuity in the 'Start' position, between the 2 applicabe terminals.

__________________
1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old

Thanks for your help.
After looking at the wiring diagram in the service manual I figured that it could only be the starter. I hit it a couple of times with a hammer and it started up. I picked up a rebuild starter and put it in. No more problems.
FIY the top bolt is pain in the ass to get to. It took a 10mm allen socket with a two foot extension to get it off. Other wise no problem get it off and back on.
Twin Oak Chef

PS Two months ago it would not start. I traced it back to a loose wire connection on the neutral safety switch. So I knew that this was not the problem.