Car — blue — drawing in constant power from only one source? (9)

I believe the answer is:

autocracy

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'power from only one source?' is the definition.
(system of government with a single ruler)

I don't understand how the rest of the clue works.

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(Other definitions for autocracy that I've seen before include "High-handed style" , "Domineering rule" , "Despotism" , "Government by one person with absolute power" , "constitution" .)

I've seen this clue in The Times.

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