Instrument electrical troubles

I have a 1988 Volvo 240 wagon, which just recently experienced electrical problems with the speedometer, odometer, and fuel gauge. My first instinct was a fuse problem, however none of those instruments were listed for any of the fuses. I noticed heavy corrosion on fuse 1's contacts, so I cleaned the contacts and replaced the fuse, and suddenly all three instruments worked perfectly.

Do these instruments operate on fuse 1 regardless of not being listed, or did I simply get lucky?

Thanks!

Yea, you got it. Good for you. A 5 cent fix.