first off, what year model, size, and brand of engine are we talking about/
Next, remove the main wiring harness plug from the engine, spin the motor over by connecting the yellow/red wire to red to activate the starter solenoid, you should have fire. Turn the key on(with the harness disconnected), check for continuity to ground on the black/yellow wire in the harness to ground, it should not have continuity to ground, if it does, you've got a wiring issue with the boat, not the engine

1994 150 Ocean Pro, where do I put these wires together (jump across plug)?

I understand what you mean about the bl /yw wire

jump the yellow red to the red at the starter solenoid