I have been working on my own cars since about 1968 and later worked as a Diesel Mechanic for 18 years. I have never had an issues with the wires sold at the Auto Parts Chain stores in any of the vehicles I have worked on.

The only time I have used really high quality wire was when for 3 years I worked for a company that bought wire from an electrical company.

The main issue is to fix any fuel or oil leaks and keep the wire away from heat like the exhaust system.

My best guess for a typical local source of better quality wiring is NAPA (lots of professional shops do business with them) next would be a store that specializes in commercial marine stuff (when a boat or ship has issues when they are out on the water it can be serious).

Note local auto auto parts stores have only fair electrical connectors.

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84 300D, 82 Volvo 244Gl Diesel