Disclaimer: I am also somewhat of an amateur

Here's the manual, in case you don't have one:

https://www.ipdb.org/files/1970/Williams_1986_Road_Kings_Manual.pdf

Go to the Switch Level test in the diagnostics menu. Instructions on getting into the test/diagnostic menus is written at the bottom of page 22, and continued on page 23 of that manual. Switch levels is described on page 26. Page 26 also contains the switch matrix, with switch names and numbers. We're going to try and determine which of the tilt switches is being activated:

• 1 (Plumb Bob Tilt)
• 2 (Ball Roll Tilt)
• 7 (Slam Tilt)
• 46 (Playfield Tilt)

Once in the switch test, you'll want to replicate the scenario that is causing the tilt in game. With the two balls out of the trough, manually hold the switch in one of the capture spots (or put a ball on it), then hold the shooter lane switch (where the ball is sitting when you plunge it). With those two switches held down, the display should be indicating that switch 39 (Ball Shooter) and whatever lock you chose. Those will be either 34 (Upper Left Kicker), 37 (Left Eject), or 38 (Center Eject). Are any other switches being indicated with those two held down? Try releasing the shooter lane a few times while the lock is still activated.

If Switch Level doesn't show you anything, try the same procedure in the Switch Edge test.

Report back if either switch levels or edge tests show switch 1, 2, 7, or 46 activating when you replicate the problem.

So if you have one ball in the trough, it's going to be activating the right trough switch, same as the upper left kicker (or do you mean it's showing as closed with no ball in there?), and the End Of Stroke (EOS) switch is what tells the ramp raise solenoid that it doesn't need full power to keep the ramp raised. I'm assuming that will be engaged if the ramp is up.

I would definitely check that diode.

From this thread: https://pinside.com/pinball/forum/topic/f-14-system-11
People on there had some good info on how to try and isolate the problem, if it's with wiring/switches/etc. on the playfield. Some other people on that thread indicated that it could also be one of the resistor packs on the switch matrix. On your MPU board in the backbox, connectors J8 and J10 are the switch matrix connections. The manual I linked to you is missing the MPU schematic page 2, and that's where it would say what components those resistor packs are (because of course it is). In my Elvira manual, it's SR11, SR13, and SR14. They're little yellow components that will be close to the J8 and J10 connectors on the board.

Also, as you start checking these switches and diodes, look for any improper wiring. The row wires (WHT-color) should be going to the non-banded side of the diode, and the column wires (GRN-color) should be going to the leaf of the switch that would transfer the signal to the banded side of the diode when the switch is closed.