Starter Solenoid still sticking, Ive replaced everything What now?

Do the checklist - pay specail attention to the testing for excessive voltage drops.


No Crank checklist for 5.0 Mustangs

Revised 05-Oct-2010 to update Fluke references.

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 both 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 know 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 unstuck 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 .5 volts across a connection indicates a problem.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf 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 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.

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.


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


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.

Bad ground can be the problem, and if your solenoid on the fender is not wired right the starter won't disengage.

Also don't throw money at it, first check everything, make sure it is in its proper workong state by testing it, otherwise you're just wasting time and moneys.

Year of Mustang? Factory style starter or retrofit?

Do the new solenoids function normally for a little while or does the issue present itself immediately?

Is the battery properly charged?

What flavor of solenoid? Some parts store stuff doesn't necessarily do too well. Napa's HD unit does decently.....

If the clutch safety switch was not closing, the test light would not have illuminated when the 'push-style plug' was tested.

If the test light illuminated (and was connected) and the starter did not engage, based upon your testing, it sounds like the fender solenoid is bad.

I hear you.

If you knew that the fender solenoid did not close while the s-terminal (push-on wire) received 12V (while being plugged into the solenoid), you'd feel pretty good knowing the solenoid is bad.

You could try disconnecting the normally-open [output] side of the solenoid (so your starter will not crank). Just put a test light on that big output lug and try the test.

The stock style sol. should mount directly in the stock location, on the fender apron. What about the clutch safety switch? Maybe its not adjusted propery, I think that they are adjustable. I think there is a positive and negative on the solenoid terminals, maybe the wires going to it are on backwards. It could be a bad ground, I don't know. For how long does the solenoid stick?

The NSS should have no affect on the starter circuit. It's for the EEC (code retrieval).

Go back and look at the typical start circuit diagram I posted.

On manual trans Mustangs the NSS is bypassed. Unless the car was an automatic converted to manual and then miswired, the NSS isn't even it the starter circuit. Only auto trans Mustangs use the NSS as part of the starter circuit.

All I can add to this is I encountered the same problem on my 89 this past weekend. My stock starter was toast so I "upgraded" to a higher torque starter from AutoZone. Even though the old solenoid was okay, I decided I'd replace that too.

The next day I install the starter and solenoid. The starter won't disengage, even with the key off. I disconnected the battery and replaced the new solenoid with the old one and it's fine.

Kdubslugga said:

Car was never an automatic, jrichker. Ive been looking and reading you diagram for days, but electrical stuff is like looking at Japanese writing. Is there any explanation as to why the car starts fine when the NSS is bypassed then?

Click to expand...

If you can't understand electrical diagrams. there isn't much more I can do to help you. Sorry, but that's a limitation on my part.