Williams multiplex the solenoids/flashers there is a relay that switches the bus voltage left or right side (A or C side). Sounds like the flashers are not wired right and getting bus voltage all the time when it should be switching. All the flashers on the C side should be common bus, but the non multiplex flashers will have a different bus. These where mixed up in my f14.

See if all of your ghosting lamps are associated with a single row or column. If so you can try a new transistor. I have seen some transistors in the lamp circuits that do no switch on and off fast enough and makes ghosting more apparent when using leds. I use a time warp to test driver boards, and each one behaves slightly different than each other when it comes to the ghosting of inserts.