My R107, 380SL '85 won't start.

The starter cranks the engine fine, so it probably must be either fuel or ignition. When I have another person start while I touch the fuel pump, I don't get any indication that the fuel pump kicks in, or runs.

Can it be the fuel pump relay? Where is it located, what does it look like?

The problem began a while ago, and after some minutes wait, the car started. Now It won't start at all.

Thank you for help

Hans