My 315 poly keeps running after everything turned off..

The way electric fans cause over-run, is that they can coast down, AKA free wheel. The motors are PM (permanent magnet) and act as generators while that is happening, causing power to flow back into the system. If the fan circuit is in parallel with the "run" circuit, it will "run on."

I don't see this happening with a fuel pump unless it's a big pump. that is because the load on the pump will stop it almost immediately