Check the zero credit switch on the credit stepper assembly...iirc it should be open if there are credits showing...

Yes as part of the credit meter.

Switch contacts can check good with a meter, but sometimes there is another path in the circuit that will give you a false reading. CLEAN all contacts & make sure the switches have enough tension to make a reliable connection.
I had the same situation & it turned out to be a flakey contact on the credit wheel.
I ran a heavy paper strip soaked with 91% alcohol between each set of contacts to remove any traces of grease, & then refaced each switch with a flexstone.
Also look for missing switch contacts - it happens.

Its a good investment when working on any EM to have an original schematic. The Pinball Resource sells full size copies for around $15.

Try here → http://www.pinrepair.com/em/index3.htm#check

Does the Coin Unit stepper reset to the zero position? It controls how many players are active (and the number of players lights).

If you trip the left coin mech switch, does a game start? (not the credit button)

If you manually trip the Start relay, does a game start?

So it sounds like there are still a few issues to work out. Here's the general startup sequence (copied from Mr. Pinball):

1. Inserting a coin or pushing the replay button actuates 'S' relay (Start relay).
2. This relay will lock-in through its own switch and a motor 2B switch.
3. 'S' relay starts the motor running.
4. 'AX' relay actuates and the 'coin' unit subtracts through switches on 'AX' and 'S' relays and switches on motor 4C and motor 1A. 'Q' relays de-energizes when 'AX' relay operates.
5. When 'AX' relay actuates, the reset relays 'Z1' and 'Z2' are energized in sequence by rivets on the 'Player' unit, through switches on 'AX' relay.
5a. Motor 1A steps the 'Player' unit, through switches on 'AX' relay and 'P5B', to the 20th position energizing 'Z1'.
5b. When 'Z1' is energized the 1st and 2nd player score units reset to zero through switches on motor 1A, motor 4A and 'Z1'. When all score units of the 1st and 2nd player are at zero the player unit steps to the 21st position through a normally closed switch on 'Z2' and normally closed switches on all score units of the 1st two players, actuating 'Z2' relay. The 3rd and 4th player score units now reset through switches on motor 1A, motor 4A, and 'Z2'. The player unit continues to its zero position through the closed switches on 'Z1', 'Z2', 'P5B' and motor 1A until 'P5B' opens.
6. When 'P5A' on the player unit closes, 'AX' and 'BX' relays reset through motor 4C and switches on 'DX', and 'R' relays. The reset cycle is now complete.
7. Inserting additional coins or pushing the replay button will step the 'coin' unit through switches on 'DX' and 'S' relays and a switch on motor 4C. The replay button circuit opens when 'coin' unit is on 4th position.
8. Place the ball in the out hole. The ball return switch closes and completes the circuit to 'O' relay through the normally closed switches of 'DX', 15th position 'Bonus' unit, motor 1C, motor 2B, 'Q', 'AX', and 'S' relays. 'O' relay locks-in. Through switches on motor 4C, 'BX', and 'O' the ball return coil actuates kicking the ball onto the runway.
9. The remaining balls that enter the outhole are kicked across the trough switch which pulls in 'P' relay. 'P' relay runs the motor. Switches on 'E', 'DX', motor 2C, 'P', 'BX', and motor 1A advances the 'Player' unit the required number of steps determined by the 'Player' unit switches and the 'Coin' unit.
10. The 3-5 ball adjustment changes the number of balls played per game. The third or fifth ball leaving the playfield will trip the 'last ball' relay 'BX' through switches on 'E', 'DX', rivets on the player unit disc, and 'O' relay.

So if you're manually activating S, but AX is not then activating, that's a good place to start. And getting the Coin Unit to reset.

Once you have the schematic for the game, then you can see the switch from S that activates AX and debug from there. And see the path to reset the Coin Unit.