Well, after 3.9 years of stupidity, I finally have a working speedometer on my 1990 Jaguar XJS... It's even accurate and matches the trip computer, and everything...!

THIS IS WHAT I DID:
I actually MATCHED the correct part number (DAC4695) from my PARTS catalog when I purchased the dial. BAM! It works. What do ya know!!!???

What's the matter with me? Go ahead. You can say it...