> nubus0 at mainbus0
> macvid0 at nubus0 slot d: formac color card II
> macvid0: Unknown video card ID 0x13a -- Not installing interrupt routine.
[snip]
> slot_noint() slot d (keeps repeating)

Ok, you need to figure out how interrupts work on this card and figure out
how to shut them off (usually you write a byte into a register). This
will require a very small amount of kernel hacking and looking at the
card's driver assembly under MacOS.

Allen Briggs put together a How-To on this subject at www.macbsd.com.

If you're not the kernel hackin' type then you'll have to settle without
the card for now.