So the game is working once the fuses were reseated. I'd say the fuse holders - but they are new - so it has to be the fuse. A fuse can measure good, but under load it may go open.
That's good to know thanks Nino, I'd assumed they'd either work or they wouldn't. I hadn't considered that they might occasionally fail under load but test ok when not.
I've had a fuse that tests fine but failed when it got warm. Found it would separate from the metal capping at one end.