Oil Pressure Switch to Sender
IF THE IMAGE IS TOO SMALL, click it.
Swapping from a factory oil pressure switch to a factory-style sender causes the factory oil pressure gauge to actually work instead of behaving like an idiot light. Ford (and some other automakers) got tired of customers complaining about fluctuating oil pressure readings and tricked-out the gauge (on trucks) in '87 by installing a 6psi switch instead of the older analog sender, and embedding a resistor in the instrument cluster (&/or wiring harness) to make the needle stay mid-scale above that pressure. Reverting to the older sender and bypassing the resistor (with a simple jumper wire) will make the gauge work as expected. It's not calibrated which is why there are no numbers, but it's still functional once you learn what your engine normally does. If the needle drops below its normal position at a particular temperature & RPM, you'll know there's a problem. But just knowing how the pressure is changing can help diagnose other problems, like rough-running. If it only happens when the oil pressure is very low, it's from the HLAs bleeding down, and the valves not opening fully.
4.9L I6 engines have plenty of room to simply install the larger sender (EOAZ-9278-A, NAPA OP6091). But on V8s, there's not enough room at the block for the sender, so a spacer is required, just like the factory used. The extension & sender will not fit with the factory oil cooler (which is useless anyway).
But common plumbing pipes are cheaper (~$2) than the machined part Ford used (~$25) which is #15 in this diagram.
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(This would be the same location to remove the switch/sender and temporarily connect a mechanical oil pressure gauge for diagnosis.)
Afterward, a wire must be installed across the oil pressure resistor. I'm not sure where the '87-91 resistor is, so it may be necessary to overlay a wire onto the harness from the switch connector at the engine all the way to the instrument cluster. On '92-96, the resistor is on the instrument cluster film circuit. I normally make the jumper wire long enough to hang down below the cluster so it can be cut if a future owner chooses to convert back to the original switch & have an idiot-gauge again.
See also:
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SSM# 19462 OASIS MESSAGE :
SOME 1997-2007 E150/F150, 1997-2007 CROWN VIC./GRAND MARQUIS/TOWN CAR, 1997-2004 MUSTANG GT, 1997-1998 T-BIRD/COUGAR AND 2002-2005 EXPLORER/MOUNTAINEER WITH 4.6L 2V ENGINE MAY EXPERIENCE AN ENGINE TICKING OR RATTLE NOISE THAT SOUNDS LIKE A STUCK TAPPET (HLA). THIS MAY BE DUE TO THE DETERIORATION OF AN AFTERMARKET OIL FILTER. VEHICLES WITH THIS CONDITION HAVE LOW OIL PRESSURE AT ONE CYLINDER HEAD ONLY, WHILE MAIN PRESSURES ARE NORMAL. DISLODGED MATERIAL FROM THE AFTERMARKET OIL FILTER BLOCKS THE CAM CAP OIL PASSAGE, EITHER AT CYLINDER #4 (RIGHT BANK REAR) OR CYLINDER #5 (LEFT BANK FRONT). FORD RECOMMENDS THE USE OF FORD APPROVED FILTERS ONLY. DAMAGE TO ENGINES CAUSED BY AFTERMARKET OIL FILTERS ARE NOT COVERED UNDER WARRANTY.
