MA/O2 Relay:

FoMoCo17

Member
Apr 1, 2011
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A while back, I copied a diagram off of www.fordfuelinjection.com (which by the way is shut down now by FORD's Lawyers for copyright infringement of protected material supposedly). Anyway, the wiring diagram was specifically labelled for 86-93 Mustangs and showed a relay titled MA/O2 Relay. It showed the left and right O2 sensor and the MAF sensor wired through it ... does such a relay exist and where is it??? The diagram also shows an ignition relay ... does it exist and where is it??? Diagram also shows the Fp Relay and EEC relay and I am familiar with them. Since i am having O2 problems checking the so-called MA/O2 Relay would be important I would think? And, after 20 years, the so-called ignition relay should also be checked and/or replaced ... so knowing where these relays are would be most helpful!!!
 
The computer power relay is mounted above the computer under the passenger kick panel.It is very aggravating to try to get to it to replace it. Removing the glove box liner and the passenger side dash speaker, along with the computer will help you get access to it. Having an eyeball on a stalk like a snail helps too...:D

Diagram courtesy of Tmoss & Stang&2birds
88-91_5.0_EEC_Wiring_Diagram.gif


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.

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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

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

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 & pinout
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
 

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  • 88-91_5.0_EEC_Wiring_Diagram.gif
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Thanks Mustang5L5 ... I think they labelled the diagram wrong with the applicable years but it specifically states 1986-1993.

The Fuel Pump Relay and EEC Relay were already changed