Assuming that you have the original transaxle in the car (not a Milano swap), there are two different types of senders that are not interchangeable. Early type has a gear drive that interfaces with a gear on a shaft in the transaxle (model year up to 85.5). The late type has an inductive pickup that reads teeth on the the shaft (model year 85.5 and 86).
If yours is the early type, I have a sender that tested functional. $30 plus shipping. Before you spend $ though take a look at the wiring at the sender. It is on the LH side of the transaxle and corrosion can take a toll on the connectors.
PM me if you are interested in the sender.
84 Spider - Long gone, but started the addiction; 85 GTV6 - Current project, Supercharged, Mega Squirt; 88 Verde - "Milo" It has a name, must be a keeper