Starter fuse? on 300E

I found my neighbor under his car this morning. He's got an 86 300E that won't start. All the lights come on, fuel pump noise, everything. When he turns the key all the way it does not turn over. The lights stay on, but the starter does not move. There is no clicking from the relay (not sure where it is) so I don't think power is getting to the starter. I'm thinking the fuse may be out, but don't know where to check. We looked in the fuse box immediately in front of the drivers seat under the hood, but they are all in tact. There was a single fuse in line for something in front of that, much larger. It was in tact. There was also a box with a red button near the battery labeled 150amp. Not sure if that has anything to do with it.

So, can anyone tell me where the starter fuse and relay is? Any other thoughts or suggestions? My only experience with european engineering is with my porsche which is a differen't beast alltogether.

It may be worth mentioning that the car has just over 230,000 miles and he did have to tap the starter to get it going before, but that was 9 years ago with no problems since.