Oil Pressure Warning Light

Oil Pressure Warning Light

What's presented here is a simple and inexpensive oil pressure warning light that can be mounted in the driver's line of sight (e.g. in an A-pillar gauge pod). While failed oil pumps aren't exactly common on 4.6, 5.4 or 5.0 engines, there have been several documented cases of a failed oil pump resulting in a destroyed engine. The intent of such an oil pressure warning light is to give the driver an early indication of loss of oil pressure so that the engine can be shut down as soon as possible, thus minimizing engine damage. Hopefully, the engine can be shut down soon enough to require rebuild rather than replacement.

This oil pressure warning light uses the voltage at the OEM oil pressure sender to control a Light Emitting Diode (LED). Accordingly, when there is no pressure at the OEM oil pressure sender, the LED is illuminated.

The following illustration shows a wiring diagram for the warning light. The entire warning light circuit consists of an LED, a resistor, a fuse block and some general wiring supplies (e.g. solder, heat shrink, electrical tape, crimp connectors, etc).

The entire warning light circuit consists of an LED, a resistor, a fuse block and some general wiring supplies (e.g. solder, heat shrink, electrical tape, crimp connectors, fuse holder, etc). The total cost for this project is about $5.00. IMHO, this is pretty cheap insurance.

Here's a parts list for items available at Radio Shack.

Jumbo Super-Bright LED, PN/276-086a, $2.59 each
Snap-In LED Bezel, PN/276-092, $0.99 3-pack
4.7K Ohm Resistor, PN/271-1124, $0.99 5-pack

Here's some basic wiring instructions.

1. Solder one lead of the resistor to the anode lead of the LED. It should be noted that the resistor MUST be attached to the anode lead. The package that the LED comes in will show which lead is the anode lead.

2. Solder the other lead of the LED to a 'GROUND' wire (e.g. 16 gauge stranded). The Ground wire will be connected to a chassis ground.

3. Solder the other lead of the resistor to a 'HOT' wire (e.g. 16 gauge stranded). The Hot wire will be connected to the OEM oil pressure sender.

4. Use heat shrink tubing or electrical tape to insulate each soldered connection separately. Then, use heat shrink tubing or electrical tape to cover both wires/leads.

5. Install a snap in bezel on the LED

6. Mount the LED assembly in a location in the driver's line-of-sight (e.g. in an A-pillar gauge pod). For the snap-in LED bezel listed above, a 9/16" hole will need to be drilled. Smaller diameter LED's and bezels are available.

7. Connect the Hot wire to the threaded stud of the OEM oil pressure sender (located below the oil filter) using a suitable crimp connector (e.g. a ring or fork tongue). Use a proper sized nut to secure the connector to the threaded stud. The threaded stud is long enough such that the slide-on connector that was originally on the threaded stud (for the dash pressure gauge) will still fit on the threaded stud even with the ring/fork connector and nut installed.

8. Connect a fuse block (1 amp fuse) in series with the Hot wire as close to the sender as possible.

9. Connect the Ground wire to a suitable chassis ground.

The above instructions are for a 97 4.6 4V Cobra engine, which has nominally 7 volts at the OEM oil pressure sender when there is no oil pressure. Presumably, these instructions will hold for all 4.6 and 5.4 engines. However, for engines other than a 97 4.6 4V Cobra engine, check the voltage at the OEM oil pressure sender stud with the slide-on connector for the dash pressure gauge connected to the stud. If there isn't a suitable positive voltage at the sender with no oil pressure, use a suitable relay to provide power to the LED, triggering the relay via the sender voltage.

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