One of the #3 targets has a switch stuck closed (either the green or yellow standups, or the white rollover).

Also be sure to check the backing blades as a possibility:
https://pinside.com/pinball/forum/topic/gottlieb-em-tech-tip-mystery-stuck-switches

Excellent. Enjoy the game.

There are three "10 point" switches and three "kicking rubber" switches that can activate the 10 point relay (N).

Then when N activates, a switch closing on N activates the 10's score reel coil. (And another switch on N activates the corresponding chime.)

Since you say that:
a) manually activating N works OK; and
b) none of the six playfield features scores the 10 points,

that would suggest a problem at the Jones plug connecter running from the playfield to the backbox.

Other possibilities would typically include N being stuck on energized (caused by a stuck switch on the playfield, or EOS switch not opening on the 10's reel), but that's eliminated by N working OK manually. Or a normally closed switch at motor 1C being open, which would prevent all 10 point features from scoring, but it would also prevent pop bumper scoring, which you don't mention as having an issue.

So based on the symptoms, the one possibility that fits is a bad connection at the Jones plug. Could just be dirty, not seated fully, or a loose wire.

But maybe there are more symptoms to find too.

Aha, trick question then!

Glad you got it sorted.