Pretty simple circuit really, Col 2 pulse from J212 - 2 on the CPU board enters the Coin Door Interface on J1-7, whene the column pulse is negative D2 will conduct current and drive Row 4 low at J1-3 on the Coin door interface and at J212-8 on the CPU board.
pasted_image (resized).png

It's possible; I do find it odd that this cable looks so different than the others connected to the CPU board; that being said, this is a signal connector and is a very low failure item as the cover over the connector not only keeps dirt out, it also keeps the wires tight in the connector so they should never get loose. The main cause of this connectors failure is corrosion from leaking batteries or storage in poor environmental conditions.

Yes, but it depends on what you have available to test this; probably the easiest thing to do is to remove J212 and use a jumper to connect J212-2 and J212-8 together on the CPU board. If switch 24 remains open at this point, the issue is on the CPU board; if this is the case, I would be curious if J208 looks like it was replaced.

If you determine the CPU is reading the closure properly, the best way to test the other side of the circuit is to use something that's both small enough to fit into the J212 connectors sockets and conductive so that you can put your meter on it...the leg from a diode or resistor works very well, you will need 2 of them, one for position 2 and one for position 8. You then measure the resistance between the two with your black lead on position 2 (GRN/RED) and the red lead on position 8 (WHT/YEL); the expected result is a very low measurement, nearly a dead short.

If this test failed, move to the coin door interface board. Remove J1 and put the black lead on pin J1-7 and the red lead on pin 3 of the header; the expected result is a very low measurement, nearly a dead short. If this test fails the problem is on the interface board, if it passes its the cable.

The cable can only be easily diagnosed to which of the two wires/connectors is not making contact...unless you have a set of needle probes that are designed to pierce the wire insulation to take measurements between the connectors in order to determine which connector is bad...most people will not have these available and will have to rely on a visual inspection of the wires at the connection points.

The answer to this is relative to what tools and parts you have available. For me this would be an easy repair that would take a couple of minutes, but only because I have both the original Pancon Mas-Con connectors that were used is the manufacture of this machine as well as the setting tool used to press the wires into the connectors. There are IDC and crimp style substitutes for this connector but I have limited experience with them.

Hope this helps.

I agree, for this connector I would leave it be, if it acts up again you can try some deoxIT on it.