88 GT 5.0 (Carbuerated) No Start


Mar 28, 2019
Hey, guys! New to the forum. I know someone must have answered or attempted to answer this question before. I purchased an 88 Ford GT 5.0 convertible from a guy who could't turn a wrench. Last season the car would fire right up on a cold start, hot start not so much. I have changed the ignition switch, HEI distributor, solenoid on fender wall, repaired a few lines that were pieced together like a 1930 barn. I have followed a few instructions found on google search, but they are for fuel injected cars. I have power coming from the yellow, brown/pink and red/green wires from ignition switch 12 volts, 12 volts from coil. I however do not have 12 volts on the red/lt green wire going to the HEI distributor. The car turns over but there is obviously no spark. I traced the wire back to the firewall, but the red/ltgreen wire does not trace back to the same wire. It was cut and runs into a larger gauge black/pink wire. When I followed the wire it goes into a connection just below the fuse box under the dash and appears to head towards the fuel pump relay. Also the Radiator fan is controlled from a stand alone switch on my console. I'm above average with a wrench but wiring is a whole other level. Any guidance would be wonderful.
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SN Certified Technician
Mar 10, 2000
Dublin GA
Since the last guy butchered the wiring, there is no standard set of diagrams or way to tell what was done. Therefore there is no simple way to see what wire goes to what device.

You will need to do one of three things:
1.) Become an electrical guru on the 88 Mustang wiring.
2.) Find an Auto Electric shop willing to fix your problem.
3.) Find an 88 or 89 wiring harness and EFI parts and convert it back to EFI.

I will post links to the 88 wiring diagrams and you may be able to work from there.
The following are diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

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.

TFI module wiring for 94-95 Mustang GT

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

O2 sensor wiring harness

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

Mustang 5.0 Lights and Radio schematic, by TMoss:

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:

Starter circuit

Alternator diagram for 94-95 Mustangs.


Mar 28, 2019
Well, after a few hours of retracing the previous owners master electrician wiring skills. I redid all his wiring and connections, putting a new negative battery cable. She fired right up. Just need to replace the fuel filter and adjust the carb its running a bit rich. Thanks for the diagrams!!
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Mar 28, 2019
Previous owner chopped the wiring harness. The red/green wire to the HEI distributor was red/yellow at the end and was covered in tubing. Spent half a day looking for a red/yellow wire until I removed the protective tubing. The red/yellow wire was spliced into the red/green and connected into a blackish/red wire. I found the fuseable link that lead to the computer at one point with a red/green wire heading to the dash. (Pics above). That’s what I ran my HEI re-wire to get 12 volts. The red/black wire he had it connected to had .54 volts and ran allllll the way to the fuel pump relay. (Pics below)


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