If you are just dealing with the pump - pull the seat to access the pump it's on the bottom (power connector is underneath so don't just yank it out
Check that you have power at the connector, before going any further. Then apply power to the pump directly to see if the pump works - could be the pump or the switch. Early 80's Corvettes used a similar system, maybe the pump is the same and can be made to work. The switch assembly is a different story as it is unique to the Fiero - the ones in the Corvette are different but maybe can be gutted and fitted to the Fiero's unit. The switch assembly can be removed, but I don't recall if it pulls through the bottom or the top (it is just held in place with the seat foam once you remove the 2 top screws). Now that I think about it, it probably pulls down due to the metal bracket for the screws.
Then there is the bladders, they may leak due to age. Rodney Dickman use to sell them and I am not sure he has any left (email him directly to ask).
To get at the bladder you have to remove the seat covers.