I guess I stepped in it. FQ problems with attitude change is usually crap in the tank, with water trapped around probes and lose hardware being the most likely trouble. Sometimes water has to be vacuumed out because sumping won’t get it. Since I wasn’t familiar with “ERR 9”, this was my first direction of troubleshooting.
Lose of power is a different type of problem. Bent pins in connectors, lose terminals, bad crimps, and even sheetmetal shavings on terminal strips and in wire bundles are things to look for. Does the gauge blank out, or does it just lodge the message? What brand gauges/system is it? I have access to BF Goodrich, Smiths and Simmons information in our line maintenance manuals, if applicable.