Wiring to any switched power is fine, including the ignition switch itself. In 1958, Chevy was still "short" on fuses. If there is a switched fuse that can be used, great.
The limited info I can find on 58 truck wiring shows no fuse for the temp gauge. I always recommend some sort of fuse for everything when a person rewires an older truck.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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