As Mr. Starkie directs you, Mr brick driver.

Use a quality stranded copper conductor wire or a proper gauge for the current that endures underhood conditions of heat, vibration, and chafing where the wire you want to install and route between endpoint connections.

It can help to also route the wire through a section of quality sheathing for auto underhood use. I'm unsure vendor brands and there quality for auto wire harness mods or additions. I have a few boxes full of conductor and sheathing.

The wire insulation temperature rating may be at minimum 80°C and if routing or pressing against the engine block or encountering exhaust port manifold radiant heat, to 100°C.

There exists conductor insulation at a temperature of varying qualities.

Bundle the new wiring you are installing to limit movement when the new wire encounters underhood turbulence.

Hope that helps.

Questions?
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Jonathan Harshman Winters III: The Mightiest, Greatest, & Most Powerful North American Comedian & Comedic Actor in Perpetuity