I would like to connect a pressure switch to the motor starter

Either the unloader valve on the pressure switch is bad or the extension cord is too long or the start capacitor is weak.
When the tank is full, unplug and try to turn by hand a few turns.
Air should come out the unloader valve drain fitting.

check and test capacitor

You contactor /motor starter has connection for up to three phase /L1 thru L3. You will be only using L1 and L2 connectors for power-in/ line and using meter find cross connector for connecting load / motor (usually white and black or red from the motor). The contactor has a push button to test your work (use meter to test before actually wiring up motor and line). The contactor is controlled by separate switch (usually pressure switch on the compressor) using proper voltage as required by magnetic switch of s-p40t. Good luck

Does this unit have a magnetic starter or just the pressure switch?Here are a few items I would check. Make sure power is unplugged. 1 - If it has a magnetic starter remove the box cover. you are checking the starter to see it has stuck closed. In the center of the starter should be what appears to be an indentation. use a screwdriver and push in on it. If it moves in and out freely it's OK. If it will not move you've found your problem.replace starter. 2 - Check the wiring to the starter. Black wire from motor should be on left bottom on overload. White motor wire should be on right bottom of starter. Incoming power should be located on top of starter left and right side. NO Starter, pressure switch only. 1 - Remove pressure switch cover. Inspect pressure switch contacts to see if they are open or closed. If contacts are open move on to wiring inspection.If closed drain all air out of tank. while draining air watch pressure switch contacts depending on pressure switch setting contacts should open around 130 - 135 psi. if all air drains out of tank and contacts do not open use a small screw driver and gently open contacts. They probably welded themselves together. If this is your problem I would get some new contacts. 2 - inspect wiring, left side of switch should have one wire from incoming power on top screw and motor wire on bottom screw. Right side of switch should have one wire from incoming power on top screw and motor wire on bottom screw. Good luck.

It will start when cold, and after driving and then parking, the starter will not turn over? Replace your starter/solenoid.

WARNING: WHEN SERVICING THE STARTER MOTOR (11002) OR PERFORMING OTHER ENGINE COMPARTMENT WORK NEAR THE STARTER MOTOR (11001) , BE AWARE THAT THE HEAVY GAUGE BATTERY INPUT LEAD AT THE STARTER SOLENOID (11390) IS "ELECTRICALLY HOT" AT ALL TIMES. BE SURE TO DISCONNECT BATTERY GROUND CABLE (14301) BEFORE SERVICING STARTER MOTOR .

2.0L Engine Starter Removal

1. Disconnect battery ground cable.
2. Remove engine intake air resonator and air box.
3. Disconnect the intake air temperature (IAT) sensor and mass air flow (MAF) sensor.
4. Remove three starter motor retaining bolts and ground wire.
5. Raise vehicle on hoist.
6. Remove integral connector retaining nuts and wires from starter solenoid.
7. Disconnect the knock sensor.
8. Remove the axle shaft bearing bracket bolts and position the bracket aside.
9. Remove the starter motor.
   

Installation
NOTE: When installing lower starter motor retaining bolts, be sure to install ground cable.

1. Position starter motor to transaxle and loosely install lower retaining bolt.
2. Install axle shaft bearing bracket. Tighten to 21 Nm (15 lb-ft).
3. Connect knock sensor.
4. Install integral connector retaining nuts. Tighten B-terminal retaining nut to 11 Nm (97 lb-in). Tighten S-terminal retaining nut to 5 Nm (44 lb-in).
   
5. Lower vehicle to floor.
6. Install starter motor retaining bolts and ground wire. Tighten to 20 Nm (15 lb-ft).
7. Install engine intake air resonator and air box.
   
8. Connect the IAT and MAF.
9. Connect battery ground cable.
   

2.5L Engine Starter Removal

1. Disconnect the negative battery cable.
2. Disconnect the idle air control (IAC) valve hose from the intake manifold.
3. Remove the IAC valve hose locator from the upper radiator hose.
4. Remove the positive crankcase ventilation (PCV) hoses from the air cleanter outlet tube.
   
5. Disconnect the intake air temperature (IAT) and mass air flow (MAF) sensor electrical connectors.
6. Disconnect the air cleaner inlet tube from the air cleaner housing and the outlet tube from the throttle body.
7. Remove the air cleaner assembly.
8. Remove the air cleaner housing support bracket.
9. CAUTION: Do not carry an open flame of any type when working on or near an open fuel system. The fuel system remains under pressure for long periods of time after engine shutdown. The fuel pressure must be relieved before performing any service to the fuel system.
   
10. Remove the protective service valve cap and connect the Multiport Fuel Injection (MFI) Fuel Pressure Gauge T80L-9974-B to the fuel pressure service valve, located on the fuel injector rail. Slowly open the valve and relieve the fuel system pressure. Remove the gauge and install the protective service valve cap.
11. Remove the safety clips and disconnect the fuel line couplings using disconnect tools D87L-9280-A (for 3/8-inch lines) and D87L-9280-B (for 1/2 inch lines). Install protective caps and position the fuel lines out of the way.
12. Remove the transaxle selector cable bracket retaining bolts and position the bracket (with cable attached) aside.
13. Disconnect the starter motor solenoid electrical connectors. Secure the battery cable harness and the heater hoses aside.
14. If equipped, remove the starter motor support bracket.
15. Remove the starter motor.
    

Installation

1. Install the starter motor. Tighten the bolts to 25 Nm (18 lb-ft).
2. If equipped, install the starter motor support bracket. Tighten the retaining bolt to 25 Nm (18 lb-ft). Tighten the retaining nuts to 17 Nm (13 lb-ft).
3. Connect the positive battery cable and solenoid harness to the starter motor solenoid. Tighten the battery cable retaining nut to 12 Nm (9 lb-ft). Tighten the solenoid terminal retaining nut to 5 Nm (44 lb-in).
4. Install the transaxle selector cable bracket. Tighten the bolts to 20 Nm (15 lb-in).
5. NOTE: Inspect all O-ring seals and garter springs for damage, prior to assembly. If either O-ring is damaged, both O-rings must be replaced. Replace the O-rings or garter springs only with the appropriate replacement parts. Lubricate the O-rings with clean engine oil, prior to assembly.
6. Remove the protective caps and connect the fuel line couplings. Install the safety clips.
7. Install the air cleaner housing support bracket. Tighten the bolts to 25 Nm (18 lb-ft).
8. Connect the air cleaner housing to the air cleaner inlet tube and the outlet tube to the throttle body. Install the PCV hoses to the air cleaner outlet tube. Connect the IAC valve hose to the intake manifold and securely tighten the retaining clamp. Install the IAC valve hose locator to the upper radiator hose. Connect the IAT and MAF sensor electrical connectors.
9. NOTE: When the battery is disconnected and reconnected, some abnormal drive symptoms may occur while the vehicle relearns its adaptive strategy. The vehicle may need to be driven 16 km (10 mi) or more to relearn the strategy.
10. Connect the negative battery cable.
    

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

SECTION 303-06: Starting System 2003 Expedition/Navigator Workshop Manual REMOVAL AND INSTALLATION Procedure revision date: 11/06/2002 Starter Motor Printable View (188 KB) Removal
WARNING: When carrying out maintenance on the starting system be aware that heavy gauge leads are connected directly to the battery. Make sure protective caps are in place when maintenance is complete. Failure to follow these instructions may result in personal injury.

1. Disconnect the battery ground cable.

1. WARNING: The electrical power to the air suspension system must be shut off prior to hoisting, jacking or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch located in the RH kick panel area. Failure to do so may result in unexpected inflation or deflation of the air springs which may result in shifting of the vehicle during these operations.
   Raise and support the vehicle; refer to Section 100-02.

1. Remove the starter motor solenoid terminal cover.

1. Disconnect the starter motor electrical connections.

1. Remove the starter motor.
   1. Remove the stud bolts.
   1. Remove the two bolts.
   1. Remove the starter.

Installation
WARNING: When carrying out maintenance on the starting system be aware that heavy gauge leads are connected directly to the battery. Make sure protective caps are in place when maintenance is complete. Failure to follow these instructions may result in personal injury.

1. Install the starter motor.
   1. Position the starter.
   1. Install the two bolts.
   1. Install the stud bolt.

1. Connect the starter motor electrical connections.

1. Install the starter motor solenoid terminal cover.

1. Lower the vehicle.

1. NOTE: If equipped with air suspension, reactivate the system by turning on the air suspension switch.
   Connect the battery ground cable.

hi there, if there is enough air pressure present in the compressor the motor will stop,the pressure switch is working.if there is a good pressure at start then suddenly lost the pressure,there is no maintaining pressure to use but on the pressure gauge appear to be have a good or enough air pressure. check if the pressure gauge have enough air pressure the motor is stop,meaning the cut out limit switch stop the motor,if you loosen the air pressure from the valve until the cut in pressure attain or meet the motor will run again there will be a cycle process of differential pressure of cut in and cut out set up on pressure switch. checking the compressor,be sure there is a high pressure on compressor and the compressor motor is stop,shut off service valve and disconnect unit device / tools from the service valve. if the compressor have enough air pressure crakc down the service valve and observe the pressure until it run again the compressor motor,if the pressure maintain the pressure you need to clean the bench, the problem is the unit device/tool you use is defective, but if the maintaining air pressure in the compressor is lost due to malfuction of motor and the compressor engine. check the pressure switch, check the motor function by loosening the belt and run the motor w/o the compressor engine if it is tripping brought it to service center, check also the lubricant oil,if neccessary change oil.have a nice day and fix my rate thanks a lot.

Your question is a bit unclear, but I assume you are asking how to wire the pressure switch in a piston compressor.

See the diagram, below.

You should have a wire from the L1 (first incoming main voltage) terminal to the pressure switch, and from the other pressure switch terminal back to the starter coil. You will also have a wire from L2 (second main voltage terminal) to the overload, and from the other overload terminal to the other side of the coil. In this arrangement, the motor starter coil must be rated at the SAME VOLTAGE as your incoming power.

This diagram works the same for single phase machines (they just don't have the third wire coming from the supply through the starter and overload to the motor.

If your machine has other safety controls (like a low oil switch), It can be wired in series with either the pressure switch or the overload.

Your question is a bit unclear, but I assume you are asking how to wire the pressure switch in a piston compressor.

See the diagram, below.

You should have a wire from the L1 (first incoming main voltage) terminal to the pressure switch, and from the other pressure switch terminal back to the starter coil. You will also have a wire from L2 (second main voltage terminal) to the overload, and from the other overload terminal to the other side of the coil. In this arrangement, the motor starter coil must be rated at the SAME VOLTAGE as your incoming power.

This diagram works the same for single phase machines (they just don't have the third wire coming from the supply through the starter and overload to the motor.

If your machine has other safety controls (like a low oil switch), It can be wired in series with either the pressure switch or the overload.

drain the air from the air receiver, and see if it switches on again