Every time I turn the key to"on" the 20A GA./IDEL fuse pops?

The only way to confirm what exactly is feed by the fuse that pops on your 1990 Chevrolet 2300 pickup is with a wiring diagram. The diagram I have shows a pink wire with a black stripe coming from what is called the "gauge" fuse. This circuit also feeds the "buzzer" and the low coolant module. I would begin by unplugging first the "buzzer" module and then the gauges cluster to see if the short goes away.