Any time the battery is connected to the battery cables there is current flow that affects the accuracy of resistance readings. Disconnect the battery from the ground cable prior to making any resistance measurements.
Troubleshooting low or missing 5 volt Vref
All tests done with the ignition switch in the Run position but the engine is not running.
The orange/white wire supplies 5 volts reference (Vref) for the TPS, MAP/Baro and EGR sensors.
Engine Mounted sensors
The TPS and EGR get their 5 volt Vref through the engine mounted fuel injector harness & the 10 pin connectors.
See the graphic for the 10 pin connector circuit layout.
A bad connection or broken wire in the engine mounted fuel injection harness is not uncommon. Check the EGR sensor orange/white wire for good 5 volt Vref. If it is good there, the TPS has either a broken wire or bad connection.
Good 5 volt Vref at the ERG sensor, then you have a 10 pin salt & pepper connecter problem or a computer problem.
Check for 5 volt Vref on the orange/white wire at the firewall mounted MAP/Baro sensor. Good 5 volt Vref there, then the problem is in the 10 pin salt & pepper connectors or in the engine mounted fuel injection harness.
No 5 volt Vref at the MAP/Baro sensor, then the problem is either a broken wire in the main fuel injector harness or the computer has died.
Remove the passenger side kick panel to gain access to the computer.
Locate the orange/white wire (pin 26) on the computer connector and check for 5 volt Vref. Good 5 volt Vref and the computer is OK.
Diagrams courtesy of Tmoss & Stang&2birds
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
No 5 volt Vref, then the computer has died. It is time to get out your wallet and go hunting…
Expect to pay $100 or more for a replacement computer. eBay has a repair service that is less expensive.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring
Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.
94-95 Mustang wiring diagrams
Mustang FAQ - Wiring & Engine Info
Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.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
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
O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif
Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg
HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif
TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif
Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif
Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif
87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif
93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif
T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg
Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg
Convertible top motor wiring
http://www.veryuseful.com/mustang/t...g/tech/engine/images/mustang88VertTopMotorCkt