Quoted from fredsmythson:
If you made sure none of the 1000 pt scoring features have closed switches, check the switch on the 1000 point relay with the black/red wire and the orange/green wire. Make sure this switch is clean and adjusted properly...
It should be open, here’s a pic of mine showing it, it’s the one on the left on the top stack That’s a lock-in switch so if those contacts are touching each other the relay will stay energized.
There are 11 total playfield switches to check, make sure you check them all. The B - O - N rollovers, the V - O - Y - A targets, and 4 1000 point rollovers.
More details here in case you didn’t look here already. Scroll down in that post for all the details on the BV 1000 relay.