Electrical 1989 LX 5.0 - No Start - Wire tracing

[Killing Hours]

Hello Stangnet!

First time poster, long time internet lurker. I've come to a point where I felt I wanted to ask my question as I haven't been able to pin down a good confirmation through various searches on the net.

** Info **

Viper 350hv alarm (Came with car purchase, looks professionally installed)
New mini starter (Confirmed working and wired by me correctly on the starter relay)
New starter relay (Confirmed working properly installed by me)
New ignition switch (Confirmed power at switch with key in run, installed by me)
T5 Transmission


So before you grab the checklist and sling it at me, hear me out.

Car started with the key when I left work, parked at a restaurant... had dinner... go to leave... car doesn't start. Naturally, I jump the starter relay with the key on... fires up and I get her home. Let the electrical fun being... right? :-|

So I go through the checklist and start eliminating things I believe could be the cause of the no start condition with a key.
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

1. Checked the starter works by jumping big posts (Confirmed working)
2. Checked the relay works by jumping hot big to small top post (Confirmed working)
3. Checked the alarm starter kill relay to ensure 12v across when the key is in start position. (Confirmed working)
4. Checked the clutch safety switch to ensure proper function. (Someone jumped it at the connector - Not getting 12v with key in start position)
5. Checked new ignition switch to ensure 12v when key is in start position (Confirmed working)

So this tells me I'm not getting power through the harness from the ignition switch to the clutch safety switch and that I'll find my issue there somewhere. So I started tracing the wires starting at the ignition switch and working my way through. Obviously the diagram isn't an exact replica of what wiring I have in the car due to the alarm but It's pretty easy to follow along anyhow.

So I trace the wire (Would be white/pink) from the ignition switch, through the alarm relay... down to the connector in the left kick panel (Getting 12v to this point) and from there it goes into a harness that turns towards the center of the car just under the drivers seat. This is where the confusion sets in for me in the diagram as it shows the wire going to the NSS (Neutral Safety Switch) which from all the searching I've done only applies to Auto trans vehicles. For manual trans vehicles, all I can find is that from the ignition switch it should go to the clutch safety switch then out to the starter relay top small post.

Also, another issue that is happening but I'm not finding a clear answer on is that the reverse lights are not coming on anymore when they 100% for sure worked prior to this.

So my question is this... On a manual trans
(A) does the white/pink run to the backup light switch and if so, (B) does the backup light switch play any role in disrupting the power to the starter circuit?

If the above is incorrect,

(C) does the white/pink follow the harness under the driver seat then turn back towards the front and go directly to the clutch safety switch? (Surely this isn't correct as there are only 3 wires on clutch connector that are all blue/light red. No white/pink on the connector at all)

As I'm typing this out, for a bit more clarity on this white/pink wire....out of the ignition a green (obviously not factory) wire goes to the alarm relay... out of the relay a solid white wire goes down to the left kick panel where it connects and on the other side of the connector the factory white/pink wire continues on. (Have confirmed 12v all the way to this point)

I know it's a wall of text and I apologize for a first post like this but I wanted to be as thorough and direct to the issue as possible. I'm trying to avoid having to rip out seats/carpet to follow the harness and figure out where the next point of failure might be in the circuit. I expected the wire to leave the ignition and go to the clutch but that doesn't seem to be the case. Thanks in advance!

 

[Killing Hours]

*** Update ***

For future readers who may encounter this problem, I believe I've answered my own question and found my problem.

https://lmr.com/item/LRS-8793MTHK/Mustang-Manual-Transmission-Back-Up-Light-Harness-87-93



It appears that my wiring harness had come loose from the mount and got snagged on something while driving... ripping it out from the underside of the car. This explains why I don't have backup lights as well as not being able to start the car with a key. Since the car was already started, I did not notice until the next time I went to start the car.

There is a built in bypass on this harness eliminating the NSS and deferring the "safety switch" to the clutch. The Tmoss diagram is a great guide to get your mind around the wiring, however, it's a bit misleading (On a manual trans) when trying to hunt down an issue like this. Hopefully this will help some future reader before they rip out the under-dash wiring and go nuts tracing wires. :^)

It may also also be a good idea to add a check for this harness into the no start checklist as well. My .02

 

[General karthief]

Good catch, glad you posted your fix, now when someone googles a similar problem they will find this (if they google their problem) and if also will show up in the 'similar threads' at the bottom of the page.

 

[jrichker]

*** Update ***

For future readers who may encounter this problem, I believe I've answered my own question and found my problem.

https://lmr.com/item/LRS-8793MTHK/Mustang-Manual-Transmission-Back-Up-Light-Harness-87-93



It appears that my wiring harness had come loose from the mount and got snagged on something while driving... ripping it out from the underside of the car. This explains why I don't have backup lights as well as not being able to start the car with a key. Since the car was already started, I did not notice until the next time I went to start the car.

There is a built in bypass on this harness eliminating the NSS and deferring the "safety switch" to the clutch. The Tmoss diagram is a great guide to get your mind around the wiring, however, it's a bit misleading (On a manual trans) when trying to hunt down an issue like this. Hopefully this will help some future reader before they rip out the under-dash wiring and go nuts tracing wires. :^)

It may also also be a good idea to add a check for this harness into the no start checklist as well. My .02

Thanks for the tip, I have added it into the No Crank Checklist as seen below.

No Crank checklist for 5.0 Mustangs

Revised 24 May 2018 to add check for backup lights harness.

No crank, slow crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of slow crank, no crank and stuck solenoid problems.

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 for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a known problem causer. Any place 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. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstick and work normally for a while.

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 .25 volts across a connection indicates a problem. The voltage drop tests need to be done while cranking the engine. It's the current flowing through a connection or wire that causes the voltage drop.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .

Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch or solenoid
100 mV Ground
0.0V Connections
A voltage drop lower that spec is always acceptable.

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 them up.

3.) Jump the big terminals on the starter solenoid 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.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

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

6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.


Starter solenoid wiring for 86-91 Mustang

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

Electrical checks for the switches and starter solenoid
Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective or the battery lacks sufficient charge to crank the engine.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.

See the Typical start circuit diagram above for wiring information for troubleshooting.

You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.

The next check is courtesy of Killing Hours.
For manual shift transmissions only: check to see that the backup light switch harness is intact and in good condition. There is a wire in the harness that loops 2 pins coming from the body side of the harness. This is the bypass for the auto transmission Neutral Safety Switch. If the connector is damaged, oil soaked or missing you will have a no crank condition. On the TMoss diagram it is the number 32 red/light blue connection jumper

Backup lights harness for 5 Speed transmission showing the bypass loop for the Auto Trans NSS
Courtesy of Killing Hours

 

[Killing Hours]

@General karthief

Nothing irks me more than running searches and finding a small tidbit of my issue but no further explanation on how to fix it. It only takes a couple minutes to save someone else hours and hours worth of frustration if people would just follow through with the fixes. I used lots o' words so hopefully it gets a good index by the search engines. Thank you for the acknowledgement.

@jrichker

Thank you so much! Glad I could finally give back to you guys for all the effort you've put in for those of us you never hear from but rely on your work.

 

[General karthief]

I use a lot of words too, but they don't all ways make sense

 

[Killing Hours]

I use a lot of words too, but they don't all ways make sense

HHAHAAAha.... My wife says the same thing to me too!

"You talk to much!" and "Ugh... you don't have to explain every detail to me (rolls eyes)"

But usually when I get to the end and ask if she understands....

"I don't get why X does Y."

My reaction: