Clue: German scientist left warning light on top of transponder (7)
Answer: LAMBERT
Explanation: Definition: German scientist
**L**(eft) + **AMBER** ("warning light") *on* **T**(ransponder) 
*Refers to Johann Heinrich Lambert (1728-77), who was born in Alsace, which was actually an enclave of Switzerland at the time, although he did spend some time in Germany.