After fixing and testing some relays in the 84, my gauge cluster has started working. The Fuel gauge needs a new sender but the speedo does not seem to work at all. Everything else works great however. Last week I was checking timing and I found that when I turn the car over with the starter motor the speedo jumps to 160 and fluctuates up there until the key is returned to the “run” position. According to the trip computer it’s done 5 miles like this. Any idea why this may have happened?
In my experience this suggests a large voltage drop. Not exclusive to Jaguars, by the way.
Poor connections, poor grounds.
Removing the cluster and cleaning all the contact points on the printed circuit, and adding a redundant cluster ground, often solves weird gauge operation.