A lot of people add toys and crap to the games. Most of the time they will connect them to J-116, J-117 and J-118 on the PDB. The game uses these connectors for the optos. When they run out of space for their crap they add in y connectors or splitters. From to much draw I have seen the pins become burnt and need replacement along with the connectors. Start here at the PDB connector and see what you get for voltage, should get 5 and @ 14.2 volts. If that's good then find the opto board under the playfield for the bookcase, check the grey/yellow wire to the ground braid, should be @ 14 volts. If good then check the same grey wire to the black wire on the opto board connector, should still get @ 14 volts. This will tell you if the ground wire is good too.