Starter Solenoid - 3 Pole To 4 Pole Wiring??

Look through the checklist and you will find your answer...

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 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 .5 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. .



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.

With the four-pole solenoid the two small posts are for the coil. One post goes to switching power the other to ground. The two large posts are for power distribution. The mounting base of the four-pole solenoid is insulated thus the need for the grounding post.

You should be able to find the three post type just about anywhere. O'reilly, Autozone, and NAPA carry them. You can also find them on eBay and Amazone. Motorcraft number SW1951C.

Saleen0679 said:

With the four-pole solenoid the two small posts are for the coil. One post goes to switching power the other to ground. The two large posts are for power distribution. The mounting base of the four-pole solenoid is insulated thus the need for the grounding post.

You should be able to find the three post type just about anywhere. O'reilly, Autozone, and NAPA carry them. You can also find them on eBay and Amazone. Motorcraft number SW1951C.

Click to expand...

That's what I like about this place: I read something and don't grasp exactly what someone is trying to do or say. Then someone else with a different viewpoint or experience comes along and nails it. I always learn something when this happens.

Good work, Saleen0679, the 3 pole and 4 pole thing just slid right past me.

Glad you figured out the S I terminals. Advance Auto etc. can bench test starters to see if the Bendix or something is sticking, For free if you take it off. Once off, a volt meter could tell if power is staying on too long too.

I just read about the S & I type starter solenoids. It appears that the 'S' terminal is used for switching and the 'I' terminal is used to bypass the ballast resistor/resistor wire on equipped vehicles and is not used otherwise. Also, if you're using a mini starter make sure it doesn't have a jumper wire between the motor solenoid and the starter. Ford cautions about run on situations on starters wired with a jumper.

Saleen0679 said:

I just read about the S & I type starter solenoids. It appears that the 'S' terminal is used for switching and the 'I' terminal is used to bypass the ballast resistor/resistor wire on equipped vehicles and is not used otherwise. Also, if you're using a mini starter make sure it doesn't have a jumper wire between the motor solenoid and the starter. Ford cautions about run on situations on starters wired with a jumper.

Click to expand...

Take a look at the diagram I posted above and see if that is what you are talking about. If so, what is the correct wiring?

Your diagrams are correct JR. I just made the statement about the jumper to reinforce what Ford and your diagrams illustrate.

When using a mini starter some use a short jumper wire at the starter mounted solenoid rather than having two long wires running to the starter from the fender mounted relay. Some people haven't had any trouble with the jumper, but Ford cautions against wiring this way. You can follow JR's diagrams above and look at Ford's Instruction Sheet to verify for correct wiring.

Sometimes starter get damaged before they get sold. One drop on the nose cone can really mess stuff up. At one place I worked, we tested all the alternators and starters BEFORE they went on the shelf. It eliminated many "irritated" customers and really cut down on warranty returns. Good luck with your diagnosis on the starter or switch. You have to be on the right track.