It's time to install a 1988 v6 oil pressure gauge sender to rectify the all-too-common pegging oil gauge problem. Somehow, I've been sent the wrong sender without the fuel pump contacts, but I'm wondering "do I really need those contacts?". Is the second set of (small) contacts in the sending unit just an emergency measure to keep the car running if the relay fails away from home, or is there another safety reason the fuel pump should run whenever the motor has oil pressure? I'm also asking if the pump contact points in the sender contributes to rapid failure of the sender as FieroSails suggests? Even though I'm very comfortable with electronics, I'm asking you experts for ideas. Thanks!

No you don't need the back up fuel pump switch located in the oil pressure sender. You can run on the relay exclusively.

The argument that the contacts are too small because the switch was designed for an oil pressure light doesn't hold water. GM designed a GAUGE SENDER to also include contacts to turn on a light? No they designed a gauge sender that was also designed to supply power to the fuel pump. If these contacts were connected to a dash light, the dash light would be on all the time the engine was running until the oil pressure failed. Yeah that doesn't make any sense. The oil pressure gauge sender with back up contacts for the FUEL PUMP has been made for decades.

The switch in the stock oil pressure sender is just a backup for the fuel pump relay. There is a common misconception that it's a cut-off switch for the fuel pump, but that's not true. Obviously, you'd lose the "safety net" if you use the pressure sender you got. But aside from that, there shouldn't be any problems.

The Ogre has a diagram of how to wire an '88 sender to replace the expensive trouble-prone ones used in earlier models. Look in the Cave.

Thanks again for your help with this :-) It's really nice to have the insight of Fiero specialists.
Hopefully changing from the old 1987 sender to this "Standard" brand '88-on unit will keep my guage working for many years.
Anyway, I was thinking of adding a fuse holder (without the fuse, of course) across the sender's fuel pump in and out wires. In the case of a fuel pump relay failure in the middle of nowhere on a dark and stormy night, I could just plug in a fuse and be on road again. When I arrive home, simply pulling that fuse will shut off the pump again. That seems easier than replacing the relay in an awkward situation... Whatja think?

If you use a weather-proof fuse holder, you should be OK. Also, keep in mind that the A/C relay (which is right there next to the fuel pump relay) is the same kind of relay. So in a pinch, you can swap the electrical plugs to get your fuel pump working again. You'll be driving home with no A/C, but at least you'll be driving home.

quote Originally posted by phonedawgz: No you don't need the back up fuel pump switch located in the oil pressure sender. You can run on the relay exclusively. The argument that the contacts are too small because the switch was designed for an oil pressure light doesn't hold water. GM designed a GAUGE SENDER to also include contacts to turn on a light? No they designed a gauge sender that was also designed to supply power to the fuel pump. If these contacts were connected to a dash light, the dash light would be on all the time the engine was running until the oil pressure failed. Yeah that doesn't make any sense. The oil pressure gauge sender with back up contacts for the FUEL PUMP has been made for decades.

I theorize that the contacts within the oil pressure switch may have been put there to lessen the load on the relay contacts but they do serve as a back up in case of relay failure. I run without the secondary circuit through the oil pressure switch on my 3800SC but use two parallel relay circuits and heavy gauge wire to supply enough current for the high demand (WOT) periods that the pump will be running.

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The stock GM 10034222 relay has contacts rated at 20A.

"3800" type relays are rated at 30A

The Fiero fuel pump fuse is only 10A. Figure half of that for the normal current of a stock fuel pump. Figure about 9A for a high volume high pressure fuel pump.