Difficult to put the jumper wire clip on the CIA chip's pin21 without completely tearing the A3000T apart, but I got it on and turned the A3000T on. Hooray! It booted to my RetinaZ3 Workbench screen. Boooo! The mouse pointer would not move.
2nd try, I disconnect the jumper wire and try to boot without it connected. Boooo again! It does not even try to boot and no HD activity is seen, can't even get to the early bootup screen (but maybe the mouse is not functional still).
3rd try, finally get the jumper wire clip attached again, in the opposite direction to be more sure that it is not touching more than the one pin it is intended to be attached to. Boooo again! Now it does not attempt to boot and again no HD activity. Damn! At least the first attempt got further than this.
4th try, I disconnect the SCSI cable from the onboard controller and both devices (hd & CDROM) and attach it to the WarpEngine SCSI-II controller.
Still no joy!
Oh well, tomorrow is another day of Amiga tweaking. I hope it will boot from a floppy.