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: