Now that is something different!
To be clear, a ball is served into the shooter lane.
5 flasher bulbs in the lamp insert turn on.
As long as the ball sits on the shooter lane switch, the 5 lamps are turned on.
Right?

The 5 lamps are probably driven by separate transistors.
Can you identify the solenoid drive numbers (first page of manual) for the flashers that are turning on?
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

My first guess is that the connector for all of those flashers is not in the right place. It should be in J125. Please check and verify that first.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

The wire colors noted above differ from what is published in the manual, which was posted earlier by @brewchap.
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Oops. You are right.
If you remove that connector, and then try the same test, the lamps do not light, right?
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Those flashers are finding ground through that connector on the driver board somehow.
You are absolutely certain that the connector is plugged into J125, right?
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Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

If the flashers on the playfield that are in parallel with the flashers in the back box act differently then something must be plugged in incorrectly. Let’s see a picture of the lower part of the power driver board.
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Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

I agree. You have flasher power connected to the flasher drive circuit. Once you make that change, the issue should be solved.

Good eye @dumbass.
—
Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info