A '42 GMC didn't come with a turn signal switch, and there was more than one approach to adding turn signals.

So the right answer might be different depending on your turn signal switch. What switch are you dealing with? Five wires or seven?

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...