Mystery starter relay WTF!

[keepinitoldskoo]

1989 5.0 manual trans... Possibly an auto swap car (A9M ECU)
Starter circuit failed.
Starter solenoid is good (I can start the engine by jumping the small terminal and the battery terminal)
Replaced and readjusted clutch switch, nothing
There is power at the white wire under the steering column when I turn the key

The big question:
I found a Ford relay way up in the dashboard that clicks when I turn the key to start. It seems to be factory installed. The relay tested ok. There is no mention of this relay in my p.o.s. Haynes wiring diagram. Wire colors are LTBLU/BLK, BLK/WHT, PNK, BLK
What is this relay connected to? I need a wiring diagram that shows how it is connected to the clutch switch and the starter solenoid.

Thanks in advance.

 

[jrichker]

No Crank checklist for 5.0 Mustangs

Revised 30-Jan-2009 to reorder checklist and add cleaning procedure for connections.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…

1.) Will the car start if it is jumped? Then clean battery terminals and check battery.
The battery posts and inside of the battery post terminals should be scraped clean with a knife or cleaner brush tool.

The clamp on with 2 bolts battery terminal ends are a know problem causer. Anyplace you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Avoid them like the plague...

A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .5 volts across a connection indicates a problem.

See Automotive Test Tools for help for help troubleshooting voltage drops across connections and components. .

2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean then up.

3.) Jump the big terminals on the starter relay next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss &Stang&2birds

AutoZone wiring diagrams

[AutoZone wiring diagrams

For 79-88 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528004e28c

For 89-93 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280069677

For 94-98 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801f5e3b

For 1999-2005 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801ef7d7

Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.

 

[keepinitoldskoo]

Thank you for your reply, however I have already tried that. Here is how I have diagnosed the problem so far:

There is no power at the solenoid's small trigger wire (Red/LtBlu)
If I short the terminal to battery power the solenoid operates so I know it's good.
There is also 12v at the WHT/PNK wire under the steering column so I know the ignition switch is good too.
This means there is a bad interrupt switch or a broken wire I need to fix.
I replaced the clutch switch and no luck


****I still do not know what the mystery relay under the dash is for and how to test the wires LTBLU/BLK, BLK/WHT, PNK, BLK***** It clicks every time the key is turned to "start" and the relay tests good (I swapped it with the fuel pump relay and it runs the pump fine)
I need a wiring diagram that shows this relay, the ones I found do not mention this relay. It looks exactly the same as the fuel pump relay.


****Where would I find the neutral safety switch wires? This car has a manual trans but I suspect it may have been an auto in the past. I checked under the center console but didn't see any****

 

[HISSIN50]

Test the mystery relay wires for continuity to ground with the car off and the connector disconnected.

Then test the wires to the relay for 12 V with the car off.

Then do it with the key turned to crank.

You should be able to see which wires show what value and what is going on. The relay either needs to energize to let the car start or it is energizing and keeping the car from starting.

 

[jrichker]

Forget about any other relays in the start circuit - there aren’t any except the starter solenoid itself. The start circuit diagram I posted is what you will find in all 87-93 5.0 Mustangs.

Typical start circuit...
Diagram courtesy of Tmoss &Stang&2birds

For auto to manual trans swaps, there is supposed to be a jumper in the lower harness that bypasses the connection to the auto trans gear selector mechanism.

Look for 12 volts at the clutch pedal switch red/lt blue wire when the key is in the crank position. No 12 volts and the jumper to bypass the auto trans gear selector is missing.

I would post the AutoZone start circuit diagram you need, but you neglected to provide the year model of your car. The wiring changed in 1991 and many of the wire colors are different.

The neutral safety switch on a T5 has nothing to do with the starter. It sole purpose is to prevent the Key On Engine Running diagnostics from running with the transmission in gear. The Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

 

[keepinitoldskoo]

Thanks again for the help
The car is an '89 LX 'vert
It has a T56 so I took the neutral sensor out of the T5, plugged it in, and let it hang. I currently have it disconnected to see if it changed the way the car runs.

If I run a wire from the WHT/PNK wire under the steering colum to the starter solenoid the engine starts (with or without depressing the clutch).

I haven't checked the mystery relay wiring because of the cramped work area, I'll try again today. It definately clicks when the key is put to "START", it looks exactly the same as the fuel pump relay and it works 100%. I guess it turns on power for the ECU, fuel, or ignition system during cranking

Starter solenoid is good, clutch switch is new, and the ignition key switch works so I guess all I am left with is a loose/broken wire.
amnit:

 

[jrichker]

As you can see there are no relays besides the starter solenoild in the start circuit. Don't waste your time chasing that and expecting it to fix your no crank problem.

AutoZone wiring diagrams

For 79-88 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528004e28c

For 89-93 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280069677

For 94-98 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801f5e3b

For 1999-2005 model Mustangs
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801ef7d7