the diagram makes sense but I am curious why there is 2 seperate wires for ground and 2 seperate wires for hot as opposed to 1 wire for each & doing the T ing inside the cup
Because the tach can be wired for a positive ground or negative, and 12V or 6V..
Means that internally the primary electrical circuits are floating
above ground..
That way it is compatible with virtually all cars, 6V negative ground for VWs & some pre-56 US cars, 6V positive ground for certain pre-56 US cars, 12V negative ground for 56 and later US cars, 12V positive ground for 56 Studebakers/Packards. Today all 12V cars are negative ground.
Just my $0.02...