Oil Pressure Switch

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Oil Pressure Switch

On this page you will see how to install a relay across the Oil Pressure Switch (OPS) that will reduce the current across the switch contacts and thus increase the life ot the OPS.

The OPS is located just behind the center of the intake manifold and forward of the fuel filter. Loacte the gray and orange wires coming up from the OPS. Cut the gray wire at a place that will let you work with both ends once cut. Just make sure you cut it before it joins into the main harness because there are other splices to this circuit in the main harness that you do not want to be on the wrong side of the splice. The orange wire will be used later

The picture shows the new relay mounted on the firewall using the screw that holds the underhood light wiring connector. You will note that I have cut into the wires coming up from the OPS on the OPS side of the connector, shown just below the white crescent on the firewall. It is not necessary to open the connector to work just peal back any tape that may be there and cut the Gray wire about 2 ins. from the conector. You can also make the splice to the Orange wire in this area.

Oil Pressure Switch Diagram

The bold lines on the diagram are wires you will install.

Install your realy on the firewall close to the OPS. Take the end of the gray wire coming up from the OPS and connect it to the common terminal of the relay. Connect the other end of the gray wire to one of the coil terminals of the relay and the other coil terminal to a good ground. Connect a wire to the NO terminal of the relay and splice that wire into the orange wire coming up from the OPS.

In this configuration the Fuel Pump Relay, original GM, will supply current to the Fuel Pump during the Glow Plug Cycle and once the engine has 4# of pressure the OPS will close and pull in the relay and supply current to the Fuel Pump through the contacts of the relay rather that directly through the OPS. This reduction on current across the OPS will greatly increase the life ot the OPS.

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