That's the coiling of the motor of the score motor. (called a "field coil", apparently)

Are you sure you plugged in all the connectors in the head? I have seen this happen in my own collection when I was newer, I forgot to plug in a tiny connector that goes straight from the playfield into the backbox and it did the exact thing you described. I am not sure if Flipper Pool has this plug as that was on a 1970's machine but since then I have seen quite a few machines with the same plug.

Otherwise, you may want to check whatever controls most of the 30 volts to the playfield, clearly you are getting some if the relay bank relays are working (controls the balls) but you are losing it somewhere else. I am assuming this game has a shared fuse between all of it so I do not think that would be it. Dirty tilt relay switch? Weird dirty hold relay issue? I don't think that last thing would allow the pool ball functionality to work, though. But I've seen games where it doesn't care, either, similar to how kickout holes are always live to make sure the ball doesn't get trapped when the game is "dark" (but on), or to make sure the ball kicks out when the game was powered off with a ball in or heading to a kickout hole. So, if that section of circuitry (the relay bank) is not wired to depend on the hold relay, I would check the hold relay. Are your pop bumpers and kickers firing? (I assume so.)

Hi JC
You should buy a schematics. I show "Buckaroo - One-Player-Replay-Pin" and "Central Park - One-Player-Replay-Pin" --- and Your "Add-a-Ball-Pin ?

On the bottom is Transformer-HOT - then upwards some switches on relays - towards top of the JPG - the playfield-stuff. "Looking-up" is so much easyer then "guessing", greetings Rolf

0Flipper-Pool-Work-01 (resized).jpg

If you can scan the schematic and attach it here in one piece we can almost certainly help you. I have lots of experience diagnosing EMs but new here so not sure if you can send me a message when the schematic is available. Otherwise, EMs (and pinballs in general) are very logical so if you like puzzles, you should do OK if you take your time.

Hi JC +
in post-3 I showed some examples --- on the bottom in the JPG is the transformer --- upwards are the connecting wires to "finally on top of the JPG the Playfield stuff like Flipper-Bats".
And the specific switches that control the wiring: These are of interest. Want to show from Your schematics that area ? Greetings Rolf

I think the jumper on the J relay is okay..
Now, when you manually press in the N Relay
(1 point), or M Relay (10 points) does it turn
the score reel? If so, you'll want to check the
EOS (End of Stroke) switches on the 1s, 10s, and
100s score wheels. Those switches should be closed,
and open when the coil energizes and the plunger is
pull in. Many times I found those switches broken.
If any are broken, that first should be fixed. Not
saying that will fix the whole problem, but it's not
a bad idea to first make sure all is good there.. (T)

Hi JC
in post-7 You write "Pop Bumpers aren't working - Sling-Shots are dead". Can You move the Flipper-Bats ? Greetings Rolf

Hi JC +
when I was writing post-3 (and showed there the JPG with switches on two different pins) I was suspecting*** "such switches controlling the connection to the many playfield stuff" - one or more are not good.
Thanks for the clarification "post-16: Flipper-Bats DO actuate". And the flipper-bats are a main thing on the playfield --- and as they work: You have proven my suspecting***: WRONG
Of course it would be interesting to see a JPG "like mine on post-3" --- but we do not need it as You have proven my suspecting "wrong". Greetings Rolf

Hi JC
I write of something good for testing --- BUT DANGER !!!
I like to use Jumper-Wires to guarantee "from HERE to THERE" IS CONNECTION.

The first test is not very dangerous. Toggle-off the pin and unplug the main power cord. Look in the pin - the transformer - see 25Volt-wire-color-red-yellow running to a fuse-holder (10 Amp Fuse).

See on the transformer the 25Volt-Returning-Wire-color-BLACK ? It is the same wire-color-black You see on one side of the coil on almost any relay. See on the transformer the 25Volt-Returning-Wire-color-BLACK ? Are You 100% sure ?
OK - then (pin is toggled off, main power cord is unplugged) establish a permanent jumper "Transformer-Lug-BLACK to "N-Relay-COIL-side-wire-BLACK-is-soldered-on". With this Jumper-Wire we guarantee "Return-Side HAS connection".
Then plug-in, toggle-on, start a game - play so the N-Relay should pull in (making 10 ? or 100 points ? on the playfield) --- Are we lucky and You get the N-Relay working ? Then the fault must be in "what we have jumpered".

No Luck --- it is getting dangerous - Toggle-off the pin and unplug the main power cord !!!
Look at The "25 Volt-10-Ampere-Fuse" - See the side of the fuse with wire-color-red-yellow coming from the transformer ? THIS SIDE IS FORBIDDEN - NEVER TOUCH, NEVER USE FOR A STARTING POINT FOR JUMPERING --- NEVER !!!
The other side of the fuseholder has wire-color-red-white soldered-on. OK - then (pin is toggled off, main power cord is unplugged) clip-on a Jumper-Wire AT SIDE RED-WHITE and take the other end of the Jumper-Wire into the open - NOT touching metal.

Take another Jumper-Wire (pin is toggled off, main power cord is unplugged) and clip-on at "COIL on N-Relay - side "not-Black" --- take the other end of the Jumper-Wire into the open - NOT touching metal.

Beware - You will use Jumper-Wires with "Power, HOT" 25 VAC. NEVER touch the gator-clips of the Jumper-Wires !!! ONLY hold the insulated wire.

OK - You are ready for the next test --- the very first jumper-wire on the returning side is still in the pin, You have two open ends of Jumper-Wires in the open - NOT touching metal.
Plug-in, toggle-on, start a game --- NOW hold with one hand one Jumper-Wire at the insulated wire and hold the other Jumper-Wire at the insulated wire --- and it is getting interesting: Hold the two gator-clips together for a moment - question: Does the N-Relay fire ?

Because the "pieces of schematics You have shown up to now" do not show the "N-Relay": In my JPG I show the Jumpering for testing "Hundreds-Score-Drum-Coil" ---- but You do testing the "Coil on N-Relay". Greetings Rolf

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JC, you are showing progress, but vhen ever a coil is staying
energized, you'll want to shut off the machine. You don't want your
coils getting very hot..
When you activated the pop bumper it stayed energized(?) When the
pop bumper coil pulls in, it should break a set of contacts that are underneath
the playfield near it's coil. You'll want to make sure that those contacts
are breaking..
Remember not to let any of the coils remain energized for more than a
few seconds..

Hi JC
the N-1-Point-Relay and the One-Point-Score-Drum in Your pin do not "talk together / work together". I show it on Buckaroo --- this works the same on Williams, Bally and Gottlieb-Pins.

My "blue R" shows "stuff used when resetting". You then play - look at the green numbers - the Score-Motor is not turning - "1" therefore is closed --- the ball closes a switch "2" worth 1 point --- the (3) N-Relay pulls-in, actuates many switches - well, closes "4" and "3" stays pulling forever***.

The "3" pulling-in also closes "11" - current flows to the Score-Drum "12" - the Drum fires - its plunger moves / travels. At end of travel the plunger opens "5" --- this cuts the connecting line for "3" - it let go and so opens "4" and "11" --- so "3" does not pull forever*** / "12" also let go and on the way back on the Score-Drum the plunger and a tooth on the plunger makes the Score-Drum step for "really making the point".

Inspect Your Score-Drum - look as the plunger travels - it MUST open a switch (my "5"). Greetings Rolf

0Buckaroo-Work-10 (resized).jpg

Just taking a stab at it, but check the operation of the tit relay and all it's switches. I once had a "Melody" that was stuck on tilt, but one of the switches on the tilt relay was closed, allowing power to the flippers. You could play it, but it wouldn't score.