Who wants BIOS now that they have UEFI???? :)
A "Bios" is a piece of software. There is no wiring diagram.
+1. The "wiring diagram" is a set of read-on-memory chips and the addressing hardware needed to let the computer read from them. (In modern machines they're usually a rewritable memory technology such as flash, so there's a bit more circuitry for that. But it's still basically the same as addressing any other memory.)