FYI
Now that I've gotten into this, it's easy to see that there are life of the car options for solving the fuel level sender problem. The gauge itself looks pretty robust if the terminals are clean throughout the circuit.
1. Replacement float-based sender assembly, 0-90 ohms, accuracy better than 5% (less than a gallon). GM made a LOT of cars with that 0-90ohm system, but never expected them to last 20-30 years and they rarely do. Replacement FLOAT-BASED senders that work well and are reliable cost only $25-30. These assemblies usually have a vertical post that must be cut to fit the depth of the tank. Simple to install, and reliable for the NEXT 20-30 years.
2. Capacitive senders, programmable. 0-90 or whatever range you wish, with much higher accuracy and NO MOVING PARTS. This approach uses a tube with internal conductors, and electronics that send a constant AC signal to that sensor. Between the conductors the fuel acts as a dielectric. There's a dielectric difference between air/gasfumes and gasoline, so as the level drops the dielectric characteristic changes and varies the circuit's impedance (think "resistance", but in an AC circuit). A simple adjustable circuit converts those impedance changes to whatever resistance range is desired. Typically, the lower and upper limits can be set.. If you have an irregular tank, some programmable capacitive senders can be calibrated for every internal level of fluid (PITA, I expect). Capacitive systems are more costly at $150-300, but it is a forever fix. Most of these can be reprogrammed to match any gauge or tank you select in the future, and can even be moved to your next car. This technology is reliable enough for aircraft, where it is standard.
Unless you buy a NOS sender that fits the original assembly, a new hole is usually needed in the top of the tank. Not a big deal, but of course you must be aware of internal baffles when picking a spot. Also, in our car the tank has very little clearance in some spots, and that must be considered as well.
Sender wiring.The original wiring can be retained because it passes only voltage - not meaningful current - so wiring is noncritical. All connections and terminals should be cleaned and prepped. I prep terminals with CRAMOLINE (Caig Industries) - a bottle has lasted me 25 years. I think the company has changed, and perhaps the name of the product, but I haven't found anything better for protecting terminals and electrical contacts.
Regarding fuel pump wiring. In many performance cars, the original wiring is replaced with 12 gauge or even 10 gauge stranded copper, to ensure adequate power MEASURED AT THE PUMP. In a Buick Grand National, I measured two tenths of a second performance improvement by replacing GM's original 18? gauge wire with a 10 gauge lead directly from the positive terminal on the battery and soldered directly to the pump terminals, interrupted by a heavy-duty relay controlled by the original fuel pump circuit.
The stock Fiero's relatively low (36-45psi?) pressure system can be served by the original wiring with cleaned terminals. But replacing the original GM wiring is a simple preventive step, and it's not difficult. If your car has a performance engine, consider that Grand National solution. It's proven, and depending on the original wiring the result will be felt and measured.
[This message has been edited by notaguru (edited 02-26-2014).]
