These are the types of problems landcruisers have sometimes.I think I already know how you know this!
I had one of those taps in place on the AGC fuse for power to the tach.
I thought of blown fuse, and then had to remind myself which fuse drives the cluster...
It's da HEATER fuse - why not?
So I checked for continuity - fuse was good! What da fuq???
Then I pried the fuse out, pushed back in - Fuel gauge moved.
Good times...
Dirt intrusion/ corrosion problems.
Clean it and carry on type problems.