Welcome to Pinside. How far does the game get through the startup sequence?:
Target Alpha Startup (resized).jpg

Does it step at all during reset?

There are lots of other topics here that might get you started including:

https://pinside.com/pinball/forum/topic/gotlieb-score-motor-spinning-on-start-up
https://pinside.com/pinball/forum/topic/gottlieb-300-score-motor-continuously-running
https://pinside.com/pinball/forum/topic/gottlieb-ice-review-score-motor-won-t-stop
https://pinside.com/pinball/forum/topic/intermittent-start-up-issue-score-motor-doesnt-stop
https://pinside.com/pinball/forum/topic/fixing-gottlieb-games-that-the-score-motor-runs

/Mark

The title of this topic is a song that’s just begging to be written
Seriously, MarkG is on the right track, so I don’t have anything useful to add until there’s more data.

Good luck, don’t give up,

Dave

If that's the case the Score Motor is likely the victim here. You might change the title of the topic.

Here's part of the schematic for the Player Unit:
Target Alpha Player Unit 2 (resized).jpg
You'll need to check the switches leading to the Add Player Unit solenoid. If nothing looks visibly wrong you could jumper around some of the switches to see if removing them from the circuit lets the Player Unit advance. If for example you jumper from the red-white wire on the right to the white-slate wire on the S relay switch and the Player Unit advances when the motor turns, then the issue is likely in either the S, PB5 or AX switches.

If the player unit doesn't advance at all during startup,
Inspect and diagnose MarkG 's circuit with Alligator clip jumper wires

https://pinside.com/pinball/forum/topic/gottlieb-big-shot-repair#post-6305153
http://www.planetimming.com/Pinball/troubleshooting/EM%20Troubleshooting.pdf
http://www.pinrepair.com/em/index3.htm#features
Example of a pinsider actually doing this https://pinside.com/pinball/forum/topic/red-baron-tech-question#post-5858156

Did you try pushing in the solenoid plunger by hand (with the power off, if you want to feel safer)? You can compare it to the step-up coil on the Replay Unit or the Bonus Unit. The diagnostic distinction here is to see if the coil can do what it should if it managed to get power.
.................David Marston

I don't understand the question. You can jumper between any two points in the circuit if your jumper wire is long enough and you understand what the jumper should accomplish. Maybe you could describe where exactly you've tried to jumper around switches.

It may be easier to jumper from the blue-white-red wire on the Z1 relay switch to the brown-white-red wire on the Add Player Unit solenoid than to try to reach there from the Score Motor. The Z1 relay is in the head too:

https://gottliebpin.com/archive/GTB-Ref/392/gtb-pb392-backbox.jpg

Also beware that that blue-white-red wire probably goes through a jones plug from the cabinet to the head. You might check that connection too.

If you jumpered across the Z1 and Z2 relay switches (blue-white-red to brown-white-red) and the Player Unit advanced that implies that the problem is between those two points in the circuit. Or, that everything from red-white to blue-white-red is working. Does that make sense?

The Z1 and Z2 relays are used to reset the Score Reels. When the Z1 relay fires it opens a switch in the "Add Player Unit" circuit and waits for the player 1 and 2 Score Reels to reset to zero. You can see that on the schematic above. After the player 1 and 2 Score Reels reset, the Player Unit takes a step, the Z1 relay relaxes, the Z1 switch closes and the Z2 relay fires and opens its switch to wait for the player 3 and 4 Score Reels to reset.

The Score Motor is probably running because it doesn't think that the Score Reels it's waiting for are zero. To figure out which reels it's waiting for you could put a non zero score on all four players, then start a new game.

Read step 5 carefully in reply #2. It describes how the Score Reels reset. When you start a new game:
- does the Z1 relay fire?
- do the player 1 and 2 Score Reels start to reset?
- do they reset to zero?
- does the Player Unit take one step?
- does the Z1 relay relax?
- does the Z2 relay activate?
- do the player 3 and 4 Score Reels start to reset?
- do they reset to zero?
- does the Player Unit take a step?

Keep in mind that just because the Score Reels show zero doesn't mean that the zero position switches on the Score Reels close.

I wouldn't change anything until you understand the problem. If the Z1 relay doesn't fire that could cause the symptoms you're seeing. There are just two switches in its circuit:
Target Alpha Z1 Z2 relays (resized).jpg
Notice that Z1 fires when the Player Unit is in position 20. Once the Player 1 and Player 2 scores reset the Player Unit takes a step to position 21 which releases Z1 and fires the Z2 relay.

This is where you ask yourself, "what switches (or other electrical devices, including connectors) do Add Player Unit and Z1 have in common?" From the two snippets of the schematic shown in this thread, we can see that both need AX to actuate. Viewed another way, the YEL-BL wire coming off a switch on AX has to have power, which then must be delivered to several points.
.................David Marston

if I understand the issue correctly, you haven't gotten to where Z1 and Z2 matters yet. Even if your wipers are mispositioned, the player unit should be stepping if AX is tripped, P5B or S switch is closed, the score motor is running and score motor 1A switch is generating pulses.

dmarston is saying the issue is an AX relay switch (because you stepped the player unit manually to position 20 and Z1 did nothing).

To test, you have two options:

1] jumper from the power rail (red highlight on schem below) to the YEL-BLK wire on the most convenient place to get to it (yellow highlight on schem below).

2] use a voltmeter with one probe on the black power rail (most coils have one lug attached to this - purple highlight), other probe on YEL-BLK and see if you have around 25VAC. If not, the AX relay switch isn't working.

3] just check/clean the AX switch with the YEL-BLK and RED-WH wires on it.

tmi:
-----
the schem chunk below is much bigger than needed. For a coil to fire, you need a path from the power rail on the right (red highight) to the right side of the coil symbol.

if using a jumper, you can attach one end to the power rail anywhere it's convenient to access ... it's all the same wire daisy chaining around.

attaching one end of the jumper to the power rail is not the only way to use a jumper, but when doing it that way you are proving you have a good path from where you put the other end of the jumper all the way to the coil IF the coil powers.

ta_issue (resized).png

ok, so you're at least to the second half of step 5b in the sequence markg has in post #2.

if the Z2 relay is unpowered, the player unit should have continued stepping then stopped at its home position. You'd need to start checking the sequence at step 6.

if Z2 didn't unpower, that would be a problem with the score reel switches. There's two switches on each reel involved in reset. One opens and stops the reel from incrementing when it gets to zero, the other is in the add player unit step-up circuit and needs to close when the reel is zero.

Can you clarify which switch you bypass to get things working? The Hold/R relay has four different switches on it.

I think the normally closed switch on the R relay is intended to fire the AXR and BXR relay coils when the game first powers up, before the R/Hold relay fires.
Target Alpha Last Ball Relay reset (resized).jpg
Once you start a game and the R relay fires the switch on the 1st Ball/DX relay should fire AXR and BXR coils as the reset sequence finishes up. Either that switch isn't working properly or the DXR relay isn't firing.

The 1st Ball/DX relay is an interlock relay like the AX relay. It has two coils (DX and DXR or DX reset) that toggle the relay back and forth with separate pulses.

jumping the switch on the R relay is cheating ... that switch should be open except at initial power on. It opens immediately when the game is reset and stays open forever. Jumping it kinda aborts the reset sequence.

it's the DX switch that should be closed to complete the path to AXR and BXR.

take a look at what the DX relay is doing. If it's tripped, push in the armature plate with your finger so the relay latches (resets / switches lift up). If that finishes the reset sequence, then as markg said the DXR coil isn't firing.

btw, the schem oopsed the label on the R relay coil symbol. It says "tilt hold relay (R)" instead of "hold relay (R)".

I see this is mostly a repeat of what mark said in the previous post ... sorry about that.

game over relay (Q) not tripping will cause the score motor to stay running.

the O relay stays powered until the ball is kicked to the shooter or the Q relay trips, and O causes the score motor to run.

the circuit path for the Q relay you need to check is the one thru the coin unit, O, BX and motor 2C switches ... assuming the Q relay trips at power on so you know the coil is good.

The Add Player Unit relay (P) is supposed to activate the Add Player Unit solenoid through this circuit
which you can Inspect and diagnose with Alligator clip jumper wires

https://pinside.com/pinball/forum/topic/gottlieb-big-shot-repair#post-6305153
http://www.planetimming.com/Pinball/troubleshooting/EM%20Troubleshooting.pdf
http://www.pinrepair.com/em/index3.htm#features
Example of a pinsider actually doing this https://pinside.com/pinball/forum/topic/red-baron-tech-question#post-5858156

pasted_image (resized).png

take a look at switches on the highlighted path below and the motor 1C switch (forgot to highlight that).

when the ball is staying in the outhole, look and see if the O relay is powered.
ta2 (resized).png

See post #34 in this thread:
https://pinside.com/pinball/forum/topic/score-motor-blues#post-6843399

the circuit in post 36 is mainly addressing the ball not leaving the outhole.

closing the outhole switch with your finger can push the switch blades more than putting a ball in the outhole.

hold a ball in there and check/adjust the switches. Make sure you have good switch overtravel - i.e. the contacts should touch before the ball hits the bottom of the outhole. The additional switch blade movement after the contacts touch makes a better connection that is somewhat self-cleaning.

if you are getting stuck figuring out the issue in howard's circuit, one way to see what is going on is to pull out the score motor service plug. That disconnects the score motor, so you can turn the score motor cams manually and watch what happens.

try not to leave the score motor in a position where a solenoid (coil with plunger) is powered for more than a few seconds when looking around, and don't do manual score motor rotation when the 120V bank reset coils will fire or you'll probably blow those fuses.

note for the player to advance, the DX relay needs to trip. Make sure you score 10 or 100 pts before activating the outhole or trough switch manually.

1] reset game and score 10 points. Verify DX has tripped.
2] remove score motor service plug
3] you can ignore the outhole if it's working ok and just close the trough switch and let go. The P relay should power and stay powered.
4] turn the score motor cams by hand until score motor 2C and 1A are both closed. See the score motor timing chart ... it will be the second time the score motor 1 switch stack lifts up. Stop turning the score motor cams.

at this point, the circuit howard highlighted should be closed and the add player solenoid powered. If it isn't, you can use a jumper wire or voltmeter to figure out what switch in the circuit is not closed.