Gauge diagnostics

All early thermal gauges were approx' 20 ohms post to post. In later models the fuel gauge only changed to 13 ohms (extended its life span).
If/when the basic 7805 regulator looses its chassis ground it will pass system voltage straight through from in to out and fry gauges. Original mechanical limiter would simply stop if/when its ground was lost.
The RTE solid state package does have ground fault protection built in its circuitry. Of course it costs more but What do replacement gauges cost? Good luck with it.