The Player 2 score lights in the backbox stay lit all the time, even in a one-player game, while the Player 3 and 4 lights work properly. The player relays and stepper contacts check out fine.

Player 2 score lights always on, even in a 1-player game: wired into the GI

Cause: The wire meant to feed the Player 2 lights (white-red here) had never been connected, and the Player 2 lamps had instead been linked into the GI circuit by a jumper wire running through several GI sockets.

Checks

• Compare the backbox lamp wiring with the schematic and find the wire that should feed the Player 2 lights.
• Look for an unterminated wire near the Player 2 lamps and for a jumper tying them to GI sockets.

Fix

• Remove the jumper to the GI circuit and connect the Player 2 lamps to their proper feed wire.

Systems

• Electro-mechanical

Games

• Champ

Related tips

• Bally or Williams EM won't light up: game over relay switch

Source: Pinball Repair help group!! (Facebook group)