1990 tracker -no start FI fuse?

[fixkick]

the thing to ponder is that you have no perfect PCB to compare., and looking at second ECU ,no idea what is there new.  acid eats copper like termites do wood, worse. my slide show has many 60a to view, even see traces that can be missing now. I advice comparing my 60a to yours. for damage to traces.

here is a 60A ECU from 80/90
burned to H3LL, and gone.
fire proof yes but not burn proof. just no flames. FR4 rated PCB prevents fire.
also there are not just 2 layers here, the inside layers failed here, ending its life forever.