And if the fuses are blown, check your wiring for shorts - don't just replace the fuses and hope for the best...
Note, I've had trouble with GM turn signals before, on my Corvettes, that were caused by a bad ground at a common grounding block in the engine compartment. Do they not work at all, or do they "sort of" work?
"Do not light up at all" and "flash three times normal ... then they start flashing really fast" are two contradictory statements. Please clarify. Maybe post a video.
Do they flash with normal brightness on the dash or are they dim? If "dim", then this sounds like the same common-ground block problem. Though I couldn't tell you where to look in the engine compartment someone else might be able to.
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