I thought this was going to be a simple, straightforward fix. I must be missing something obvious. I could use some suggestions.

So my TAF was working fine. I fired it up and when I hit Start I got the "Pinball Missing" error. My guess was a bad trough switch. I went into switch tests and found that the right trough switch did not close when the ball hit it. I checked for loose wires or something obvious and saw nothing. I ordered a replacement switch and diode from Marco. I installed the switch with the diode the same direction as the one I removed, green-brown to center tab, white-violet to the blade side tab. I expected this would do it, but the problem still exists.
I did continuity checks from left trough to center trough to right trough through the green-brown wire and it checked. Then I did continuity checks on the white-violet wire from right trough to ball shooter to right sling to center swamp and they checked.

I am not sure now to check one of these micro switches but I put the meter on the tab opposite the blade end and on the middle tab. The switch show open and closes when the blade is pushed. In the game, in test mode, the switch is not registering a close even though I put the meter on the same two terminals (as above) with it in the game and the meter see the close, but the game does not.

Am I checking the switch wrong or is there something else I should be trying?

Not sure what you are suggesting I short. Am I to take another diode and put it on the green-brown to the white-violet? If so, does it matter which is the banded end?

If the problem was the CPU U19-5 (white-violet row) wouldn't the other switches on that row have problems? Same question about CPU U20-18 (green-brown column) wouldn't the other switches on the column show errors? Or doesn't it work that way?

On the white-violet row the Right Trough (17) does not register (this is the one that would give me the pinball missing error), then switch 27 Ball Shooter also does NOT register. I need to check the Right Sling(37), Center Swamp(47), etc on this row. I did check continuity between them but did not think the do the single switch test on each of these because I was not getting an error report on them. I assumed they were working. I can see why checking these is important.

When I checked the switch that I removed it was bad. It never indicated a close so that is why I figured I had this nailed.

So here is another question. Can switch 27 or its diode cause switch 17 not to register? I have the parts to replace that switch if needed.
I will be away for the next week and a half so I can not check 37, 47, 57, 67, 77, 87 on that row right away.

Thanks for the ideas and I'll report back.

I took the apron off. While in the switch test mode I loaded the balls. I still had the dmm on the switch and the meter saw the closure but the game did not register the closure. I pushed the switch manually and the game did not see it close. Had it registered when I pushed it manually then I would have suspected the blade position. I may need to revisit this once I get the switch to somehow pass the test.

The column switches Left Trough (15), Center Trough (16), Start Button (13) work in the switch test. I did not check Plumb Bulb Tilt (14), but I assume it works okay if the others in the column works.

In looking at the "7" row, if 17 (Right Trough) is first in the row, does that mean that it should have a white-violet wire going directly to the J208-8 on the board? Or can the wht-vio wire from the board go first to any of switches in the row? Just trying to figure out how these things are actually hooked up.

Thanks, good article and it is helpful. More than just fixing the game, understanding how and why is important.

I got a chance to check the game out thoroughly. Half of the switches on row 7 worked and half did not. So it had to be a loose/broken wire. I found one of the white-violet wires had come off of the Thing eject hole switch. Soldered it up and everything is now working. Thanks for the help guys.
One followup question. One of the switches in row 7 is a set of lane optos. I did not know how to check continuity to these things because the white-violet wire does not go directly to the optos. Can someone tell me how the optos are wired on row 7. They work fine, but I could not figure out the wiring for these things.