Starter Trigger Wire...no Power

broncojunkie

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Apr 12, 2014
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I just finished a rebuild and some engine bay work on my 88gt. While I was at it, I did a few upgrades, including a maf swap. I'm having an issue with starting. It will turn over if I put 12v to the starter trigger wire post on the fender relay, or if I jump the relay. But I'm not getting power to the trigger wire when I turn the key. Everything worked fine before dismantling it. Ignition switch is only a couple years old and appears to be in good shape. I've been looking through wiring diagrams and although a few wires still have me stumped (not on the diagrams or hard to tell color due to fading from age), it looks like everything is ok.

I was hoping someone here could help point me in the right direction. I'm sure I'm overlooking something simple. Or should I just try a new ignition switch?
 
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jrichker

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No Crank checklist for 5.0 Mustangs

Revised 24-Oct-2013 to update voltage drop figures.

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. .

attachment.php?attachmentid=64167&stc=1&d=1286329941.gif


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
attachment.php?attachmentid=21328&d=1080916057.gif



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
attachment.php?attachmentid=52294&stc=1&d=1192414749.gif



Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.
attachment.php?attachmentid=53216&stc=1&d=1201020653.gif


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.
 

broncojunkie

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Apr 12, 2014
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J,
Thanks for posting this. After working on this car all week, my brain is about as fried as the battery I just replaced lol! I finally got the car running. First, I had a couple grounds that were hooked up wrong. I got them straightened out and then dealt with the battery, which had evidently gone bad after sitting since last summer. Then, the fuel pressure regulator was leaking from a bad diaphragm. Next, I had to fix the firing order, which I had set up backwards (another late night, fried-brain screw-up). Reading through your post made me realize that the problem likely has to do with the clutch switch.

The clutch switch had been bypassed at some point before I purchased the car. I'm guessing I plugged in or otherwise connected it somehow while installing everything. I'll need to do some research and see if I can figure out where the connection is for the switch, so I can possibly bypass it like it was.

Thanks for the help!
 

General karthief

wonder how much it would cost to ship you a pair
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There are two switches on the clutch, one is a starter safety switch, the other is for computer reference, works in conjunction with a switch on the trans,
You should have to push the clutch pedal to the floor for the starter to engage, you really don't want to bypass this one.
 

broncojunkie

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Apr 12, 2014
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Yeah, I can see it being a safety issue, however, I've driven probably dozens of cars over the years without a clutch safety switch. In fact, I currently have 3 mustangs that came equipped with no clutch switch. So I'm not too concerned about it.

But after looking it over again, I'm now thinking that the problem does, in fact, lie in the actual starter switch wiring. My wire that comes from the ignition switch to the starter relay doesn't go straight to the starter relay like most of the wiring diagrams show. Instead, it goes into another relay, which is mounted to the rear of the drivers side shock tower. I'm not getting any power whatsoever to that relay. It should be getting power...either constant or at least switched. The wires from that relay appear to go back into the harness, not directly to the battery or starter relay to grab power. The "trigger wire" on the starter relay can be traced back to this other relay, I just can't tell where it's supposed to be picking up it's main power source.

I'm not sure this relay is factory, as the wiring around this area is a little rough. It has obviously been altered at least a couple times, with some added/spliced/replaced wires here and there. I'm going to have to try and trace some of it back to the ignition switch when I get time, I guess.
 

broncojunkie

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Apr 12, 2014
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I might want to add that at one time, there was an alarm system installed. It had been unhooked before I got the car, but some of the wiring remained (unhooked, but still found under the dash and center console). That could be the reason for the additional relay, if it isn't a factory one.
 

broncojunkie

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Apr 12, 2014
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Well, I traced wiring all over the car. I was losing signal somewhere inside the dash. So instead of tearing everything apart, I just tapped into the correct wire underneath the column and ran a new wire straight to the starter relay. Works great now. At some point, I plan on cleaning up the wiring in the drivers side engine bay. It definitely needs some attention. Thanks for all the help. I'm getting ready to take her on her first ride since tearing the motor out last summer. I'm curious to see how big of a difference the heads, cam, intake, maf, etc are going to make!