Do you have a schematic? You'll have to find the relay or switch contact that energizes the 0-9 coil. A schematic will help.

Rome N.Y. Not so far away..
Okay, I take it that the 1st Player 0-9 score reel resets okay.
You might want to inspect the wires (solder joints) on the Player-
Step-Up Unit. Also, I'm thinking the Player-Step-Up may have the
spring loaded wipers. If so, you'll want to make sure that none of
those spring loaded (known as snowshoe wipers) aren't a little sticky
and they are moving freely.
BTW: Is your machine a 2 Player machine? (T)

Yes, your machine looks to be from the early 50s. Looks like it has the 6" pins, so the Player-Step-Up wouldn't
have the spring loaded wipers. I'm not sure what that added note means, but probably best to just ignore and
hopefully the machine is in its natural physical state..
After firing up the machine, you can manual activate the 0-9 Score Relay to energize the 0-9 score reel. If I
remember correctly, I don't think each individual player's score reels have separate circuits going through the
plugins', but you can try re-seated them.
Where it does separate the circuits to the players is in the Player-Step-Up-Unit. If all wires seem fine on the
1st players 0-9 score reel and on the P-S-U-U- (Player-Step-Up-Unit) and the wiper is making good connection
on the P-S-U-U's wiper board, you might want to inspect the backside of the wiper board to make sure all
connections look good there, especially the ones where the wiper blades are on the rivets when it's in the 1st
player's step-up position. If all fails, then jumping wires would be the next thing to do..
I actually plan on going to Canastoda, but not until Spring. But for now, I would maybe consentrate a little more
on the P-S-U-U, and the circuitry wiring from the 1st player's 0-9 score reel to the P-S-U-U-..

Glad you found it!
It's those type of problems that aren't on the schematics that can be the tricky ones..