Starter wont disengage once started

What year is the car? Did you just change out the starter or did this problem show up on it's own?

What style starter? Piggyback solenoid? If so, was the solenoid wired/rewired for the piggyback solenoid? If not, inductance can cause the starter to run-on.

Otherwise, I would put a test light on the fender solenoid trigger and watch it after you let off the key. If the light goes out but the starter runs-on, the issue is likely from the fender-solenoid to the starter. If the light stays on after you let off the key, trace back towards the ignition switch.

When you say 'OE', is it the 91 older or 92 newer starter? Maybe you can post a pic of your starter solenoid so we can check your wiring there. If you said that the starter engages when you turn the key to 'run' and keeps spinning after the engine starts, then you must have it wired incorrectly no matter what style starter it is.

91 older style

92 newer style

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.

Great info !!

lxman said:

Thanks I will definetley check into the connections. Its just frustarting that this is the only thing holding me up now!

Click to expand...

did it ever start correctly after you did the conversion or is this an issue that just ocurred?

I'm lookin' real hard at that itty bitty pic, and if something's shorting between those two big terminals, you'll get the exact symptoms you're describing... or maybe the starter would run all the time.

Just to get your mind workin', I also have an LX, was a 4 cyl. with the stock OE starter, battery in the trunk. The starter took a crap so I replaced it and decided to put a new solenoid in too. After replacing the old solenoid with the new one, I got the same problem you did, so I put the old one back in, works fine. I have no idea why.

It engages when you turn the key to on? Sounds like something is crossed up between the dash and the engine bay. It shouldn't engine until the key is turned to start, obviously. Can you confirm that you have 12 volts at the small wire going to the small post on the starter solenoid when the key is in the on position?

Take the wire off the solenoid first to test, naturally.

So, this thread actually solved one of my problems. I have a 92 with the mini starter, and I've never had one of these before. The starter would always hang for a second or two after starting. The previous owner had this problem and couldn't figure it out. I couldn't find anything obviously wrong either.

Well, the large and small wires going down to the solenoid on the starter were both connected to output of the firewall solenoid.

I moved the large gauge wire over to the battery side of the firewall solenoid per the diagram. Bingo, no more hanging starter.

So what would have caused this? My first guess is maybe capacitance in the wire would keep the solenoid on the starter energized for a second. Hissin mentioned something about inductance though, is this the situation he was referring to?