Tools needed: DVM (Digital Multi Meter) or multimeter, 1/2" wrench, 2 safety pins.
The safety pins are used to probe the wiring connectors from the wire side.
Make sure you know how to correctly use a DVM or multimeter.
Resistance checks:
Do not make resistance measurements with the battery ground lead connected. You will get
incorrect results and possibly damage the DVM or multimeter
Do not test the white/black wire at this time.
With the battery ground cable disconnected from the battery, use an ohmmeter to check continuity
on the wires. Turn the key to the Run position and place one ohmeter lead on the positive
battery cable and the other on each of the wires.
EDIT: All wires should read less than 1.5 oms, except the lt green/red wire, which should be 100-500 ohms
Testing the white/black wire:
Use the safety pins to probe the wiring connectors for the white/black wires or
disconnect them and probe the connector from the front side. You shoul see less than 1.5 ohms.
Voltage checks:
Carefully re-connect the battery cable postive termnial to the battery at this time.
Make sure that it is clean and tight
With tht stock alternator, you should see battery voltage (12 volts or more) on the black/orange,
yellow/white and lt green/red wires with the ignition switch in the run position. All measurements
are taken at the alternator.
No 12 volts on the black/orange wires - fuse link probably open
No 12 volts on lt green/red wire - dash indicator burned out, and 500 ohm resistor open circuited
No 12 volts on yellow/white wire - fuse link probably open
Diagram courtesy of Tmoss & Stang&2birds
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring
http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.
Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif
Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg