I thought we controlled both gauges by regulating the negative side through a variable resistor or sending unit. What it looks like is the negative side of all the gauges somehow got tied directly to ground.
The chances of BOTH gauge senders becoming grounded is nearly zero
This is a simple series circuit
power from the key --- voltage limiter unit -- to BOTH gauges (Y)
power to fuel gauge, through gauge, to sender, to ground
power to temp gauge, through gauge, to sender to ground.
If something goes wrong with the voltage limiter, and it sends too much pwer to the gauges, they will peg. This is CLASSIC limiter failure. Ford and Mopar both used essentially the same system. It's happened to me at least three times over the years in different cars
