I'd follow along with a meter set to AC. See where you have power and don't. Maybe a weak connection dropping voltage but passing continuity ?

LTG : )

Study up on it. AC you measure hot to common, not hot to ground.

LTG : )

Are the GI connectors on the interconnect board in good shape and any signs of burns?Have you tried reseating those GI Connectors?
Also pull out the 4 fuses located next to the above connectors and test with meter

You mentioned changing out relay for new. Good.

However, make sure that connector attaching to the relay is good in terms of its wiring being seated into the connector well.

Sometimes one of the wires pulls out of the connector ever so slightly. I’d turn game on and jiggle that connector carefully and see if gi flashes at all. Push on the wires inserting into that connector.

J6 J7 J9 On tbe interconnect board , check those for burn up. Also pull the 4 fuses located next to the above connectors. and check them.