No Start
Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…
Check battery, terminal connections, ground, starter relay switch (also known as solenoid) and starter in that order.
A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection: more than .5 volts across a connection indicates a problem.
See
http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103 for help
1.) Will the car start if it is jumped? Then clean battery terminals and check battery.
2.) Check the battery to engine block ground, and the ground behind the engine to the firewall.
3.) Then pull the small push on connector (red wire) off the starter relay (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it starts, the relay is good and your problem is in the rest of the circuit.
4.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then the relay is bad. See
http://www.autozone.com/images/cds/gif/large/0900823d80195963.gif for 88-90 year cars .OR see
http://www.autozone.com/images/cds/gif/large/0900823d80195964.gif for 91-93 year cars. See
http://www.autozone.com/servlet/UiB..._us/0900823d/80/1d/db/3c/0900823d801ddb3c.jsp for 94-95 model cars.
5.) Jump the big terminals on the starter relay next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.
6.) The starter may be hung, loosen up the bolts that hold it on, and give it a good whack with a big hammer. Tighten up the bolts and try again.
7.) If that doesn't work, use a jumper cable from the positive lead on the battery direct to the starter post where the big wire from the relay connects. If it cranks then, it is the power wire from the relay gone bad. This will be hard to do, since there isn't much room to do it.
8.) Pull the starter and take it to Autozone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.
Fuel pump doesn't shut off
In a properly functioning car, the ignition switch turns on, then the ECC (computer) relay, then the computer powers up.
The battery sources the power to the fuel pump through the fuel pump relay. The fuel pump relay control coil gets power from the computer and the computer completes the circuit by providing a ground. This closes the fuel pump relay contacts. Battery power then flows through the closed relay contacts to the fuel pump.
The computer is programmed to turn the fuel pump relay on and off according the needs of the engine.
You have one of four problems:
1.) A failed fuel pump relay: relay contacts have stuck closed.
2.) A short to ground in the computer to fuel pump relay control circuit. The fuel pump relay is located under the driver's seat. The green wire going from the fuel pump relay to pin 19 on the computer may have a place in it that has rubbed bare and is shorting to ground. The computer test connector under the hood on the driver's side of the engine also has a wire that connects to pin 19 on the computer. It is used to test the fuel pump circuit by grounding it to make the fuel pump run all the time. If someone jumpered it to ground, it would be just like a short to ground.
3.) Someone has crosswired your car. This could be difficult to fix, since the bad wiring could be hidden in a number of different places.
4.) Failed computer - not very likely, since the computers are not prone to failure.
See
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif for Tmoss's wiring diagram
