what will cause the gages to go all over the place and shut off engine?

What is your question?

key in on, engine not running new purge valve clicking open n close with gages going to needle stop and than back fast over n over ( mostly gas gage but other move as well ) before stopping, lost of power when get started and shuts off. ran good before three days of rain.

What makes this problem better or worse?

running engin

How long has your 1997 GMC Savana 3500 had this problem?

day