Wiring rear turn signal resistors.

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I recently put GTR (3157) and these are the 1st pair of lights I’ve ever installed that flickered. I have resistors to wire in but don’t know what colored wire to tap into with the black - wire. Any help would be greatly appreciated. I don’t have access to a tester to truly test it out. I was guessing the yellow wire would be designated for the turn signal. Just want to make sure.

I was unsuccessful finding anything else about this topic. TIA