modern cars use carbon fiber cores..to prevent to much RF noise .
not recommended for outboards
get yourself some good solid stranded wire core at a local motorbike shop, amazon or tractor supply store 4 feet should do… some places sell it a $1/foot
Listen to Cosbyman and Frank! Use plain old 7mm copper core wire. You can get it a lawn mower repair shop , tractor repair shop or even an auto supply shop.
Cheers,
Cajun