Learn Swedish: Om du inte blinkar, så underkänner inspektören dig på uppkörningen. - If you do not indicate, the inspector will fail you on the driving test.

The word så acts as a resumptive adverb here. It steps in to represent the entire 'if' clause that just happened, acting as a bridge to the main clause. It is completely optional but very common in spoken and everyday Swedish to make the transition smoother.

If we drop så, does the word order of the main clause change?

No, it stays exactly the same: underkänner inspektören dig. Because the entire subordinate clause (Om du inte blinkar) counts as the first block of information in the sentence, the V2 (verb-second) rule dictates that the verb (underkänner) must immediately follow it, regardless of whether you use så or not.

Why is the word order inte blinkar instead of blinkar inte in the first half?

Because Om du inte blinkar is a subordinate clause. A key rule to remember (often called the BIFF rule) is that in subordinate clauses, sentence adverbs like inte always come before the finite verb.

How does blinkar mean 'indicate'? Doesn't it mean 'blink'?

Yes, att blinka literally means to blink with your eyes. However, in a traffic context, it is the standard verb for using your turn signal. The physical indicator on the car is usually called en blinkers.