1968 Shelby GT500

Wiring Harnesses

This page is about the most popular 88-93 Mustang 5.0L HO Mass Air EFI system.
Other 5.0L Car computers
Truck computers
4.6L, 5.4L and other Modulars

If you would like to learn how to build your own EFI harness you will need to know:
How to Solder
What Wire Sizes to Use
How Relays Work
How the EEC Computer Connector Comes Apart
Changing the Injector Firing order
Then study the wiring diagrams, computer pin out charts, and assemble your own harness.

If you want to purchase a BRAND NEW EFI harness or buy parts for your harness project;
Please visit our PRODUCTS PAGE

Pin #
Wire Color
Connections for a 88-93 5.0L HO Mustang
Value at Idle
01
YEL
+12 Battery Voltage
12-14 volts
03
DG/WHT
VSS + / Vehicle Speed Sensor Positive
55MPH = 125hz
04
DG/Y
IDM / Ignition Diagnostic Monitor (TFI)
20-31hz
06
ORG/YEL
VSS – / Vehicle Speed Sensor Negitive
55MPH = 125hz
07
LG/RED
ECT / Engine Coolant Temp Sensor
0.5 volts = 200*F
09
TAN/BLU
MAF RTN / Mass Air Flow Return
< 0.1volts
12
BRN/YEL
Fuel Injector 3
4.9-5.2ms duty cycle
13
BRN/BLU
Fuel Injector 4
4.9-5.2ms duty cycle
14
TAN/ORG
Fuel Injector 5
4.9-5.2ms duty cycle
15
LG/ORG
Fuel Injector 6
4.9-5.2ms duty cycle
16
BLK/ORG
Ignition Ground (TFI)
-
17
TAN
MIL / Engine Light & STO / Self-Test Output
ON = GND
19
DG/YEL
FPM / Fuel Pump Monitor
Pump on = 12-14volts
20
BLK
Ground
< 0.1volts
21
WHT/BLU
IAB / Idle Air Bypass
3.0 – 12.0 volts
22
BLU/ORG
FPR / Fuel Pump Relay
ON = GND
25
GRAY
ACT / Air Charge Temp Sensor
3 volts = 70*F
26
ORG/WHT
Voltage Reference
4.9-5.1 volts
29
DK GRN
Right HEGO
0.0-1.0 volts
30
BLU/YEL
Transmission Neutral Interface
0.0 volts in neutral
36
YEL/LGRN
SPOUT / Spark Output Signal (TFI)
-
37
RED
EEC Relay +12 volts
12-14 volts
40
BLK
Ground
< 0.1 volt
42
TAN/RED
Fuel Injector 7
4.9-5.2ms duty cycle
43
DK BLU
Left HEGO
0.0-1.0 volts
45
GRN/BLK
BP / Barometric Pressure Sensor
159hz = sea level
46
GRY/RED
Signal Return
0.1 volts
47
DK GRN
TPS / Throttle Position Sensor
0.9 volts
48
TAN/RED
STI / Self-Test Input
GND = Self-Test
49
ORG
Ground
< 0.1 volt
50
BLU/RED
MAF / Mass Air Flow Sensor
0.8 volts
52
LT BLU
Fuel Injector 8
4.9-5.2ms duty cycle
56
DK BLU
PIP / Profile Ignition Pickup (TFI)
-
57
RED
EEC Relay +12 volts
12-14 volts
58
TAN/RED
Fuel Injector 1
4.9-5.2ms duty cycle
59
TAN/ORG
Fuel Injector 2
4.9-5.2ms duty cycle
60
BLK
Ground
< 0.1volt

Fuel Injection Harness Ingition Circuit:

Signal Return Voltage Reference Ground +12 Battery Voltage +12 Run Voltage
EEC 46
Self-Test
MAP or BP
TPS
ACT
ECT
EEC 30 (MT only)
EEC 26
MAP or BP
TPS
EEC relay
Ignition relay
MAF/O2 relay
EEC 20/40/60
EEC 49 (hego)
EEC 30 (AT only)
TFI shielding
HEGO’s
MAF
EEC 1
EEC relay
Fuel Pump relay
Ignition relay
MAF/O2 relay
EEC relay
Fuel Pump relay
Ignition relay
MAF/O2 relay

Fuel Injection Harness Power circuit:

 
EEC Relay
Ignition Relay
MA/O2 Relay
Fuel Pump Relay
Pin 30
Constant +12 Volts from Battery protected by Fuse
Pin 85
Ground Ground Ground EEC Pin 22
Pin 86
+12 Volts from Ignition Switch (Hot in Run and Start)
Pin 87
EEC 37/57
Ck Engine Light
Fuel Injectors
Idle Air Bypass
TFI
Coil
MAF
R HEGO
L Hego
Fuel Pump
FPM (EEC Pin 19)

Helpfull when installing the Ford Racing Performance Harness M-12071-C302:

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