Seeing as how your eject hole works, it's nothing to do with J1p4. If it were anything on that connector, that solenoid wouldn't work.
I would use a voltmeter to check for voltage at the origin of the Blk/Grn wire, the sockets of the flashlamps, and at both sides of D38. In DC Volts mode, put red lead at each of those points, with black lead attached to grounding braid somewhere else in the game.
Put the game in diagnostic mode, in the flasher test, on solenoid 5C. Power is coming in at each of those points and the machine is periodically supplying ground to them to complete the circuit and make them flash. Therefore, you should see DC voltage at each of those points that periodically falls to 0V. You'll be able to narrow down where the break is by seeing where you stop seeing voltage.