not 100% sure here, but i believe the 84 uses the same bulbs as the 87 #882 halogens very expensive like $10.00 each
I retro'd mine to use the 194's, $1.97 for 2, available at any autopart store, walmarts, radio shack etc.
a bit of work to do that (the retro fit), but in the end, the 194's are readily available, and very common
as a side note the 882's being halogen, are very hard on the circuit board, and will/have actually burn(ed) it ( due to the heat), you will see this effect when you first open the cluster. Also the 194's do not require any handeling precautions like the 882's
The 194's do give off slightly less light than the 882's but not enough differance to bother anything.
for me the bottom line was component longevity, so out for the 882's and in for the 194's