Quoted from TZ:No ground when all connectors are removed. Is this correct?
If the game has incandescent lamps then you will measure around zero ohms to ground at TP1.
Incandescent lamps have very low resistance and lots of them in parallel reduces the resistance.
Inspect the stapled braid wires behind the door/display door to see if there's a short to something else. From memory it can happen on the lower corner of the door where the Game Over lamps are if the socket tab touches the metal door rest in the head that's grounded.