STARTER TEST 2: Verifying The Start Signal
So far in TEST 1, you've confirmed that the starter motor is ok and cranking the engine (when applying 12 volts to the starter motor solenoid S terminal with a remote starter switch).
The next step is to see if the starter motor solenoid is getting the Start Signal on the S terminal wire. Since you already have your vehicle up on jack stands... this test won't be that hard to do.
Here's what you'll need to do:
Lift the vehicle and place it on jack stands (if it isn't already up in the air). Now, while underneath the vehicle, place the RED multimeter lead on the S terminal of the starter motor.
The S terminal is the smallest stud on the starter solenoid. To this small stud, is attached the wire that comes from the Neutral Safety switch and which delivers the crank signal from the ignition switch.
Attach the BLACK multimeter lead to a clean and rust-free spot on the engine or on the vehicle frame.
Here I'm going to recommend something to you: Use a battery jump start cable to ground the BLACK multimeter lead to a clean ground point on the engine. The reason why is that depending on how rusty and dirty the underneath of the vehicle... you may NOT be able to find a clean and rust-free spot to ground the multimeter's BLACK lead.
Now, have your helper hop inside the vehicle and turn the key to crank the engine.
Now, the engine won't turn over, but the idea is to verify that the starter motor solenoid is getting an activation signal from the ignition switch.
Your multimeter is going to register one of two results: Either 10 to 12 Volts DC or no voltage at all.
Alright, let's interpret the results of this test...
OK, let's make sense of the readings that your multimeter recorded in the test:
CASE 1: If your multimeter registered 10 to 12 Volts: This test result let's you know the starter solenoid is receiving the activation signal (crank signal).
This means that we can forget about the Safety Neutral switch and the ignition switch being BAD. OK, now the next test is to do a very easy and simple voltage drop test. Go to TEST 3
CASE 2: If your multimeter DID NOT register 10 to 12 Volts: This result exonerates the starter motor. Your starter motor is not BAD.
Here's the reason why... without this crank signal, the starter motor will not crank the engine. Now, although it's beyond the scope of this article to test the Neutral Safety switch or the ignition switch, you have eliminated the starter motor and this means saving money by not buying a part your vehicle does not need.
STARTER TEST 3: Voltage Drop Testing The Battery (+) Cable
In this starter motor test step, you're gonna' verify that the positive battery cable that attaches to the large stud on the starter solenoid is supplying all of the battery's power to the starter motor.
Here's why... corrosion somewhere on the positive battery cable, either at the end that connects to the battery positive post or on the end that connects to the starter solenoid could be causing a voltage drop.
In this case, a voltage drop is simply a condition in which only some of the battery power is reaching its final destination, mainly due to some type of corrosion. If this happens on your Ford vehicle, the starter motor will not be able to crank the engine, even though the battery is in a fully charged state.
Place you multimeter in Volts DC mode. Attach the RED multimeter lead to the center of the positive battery terminal. If the positive battery post isn't clean... clean a spot right on the top of it. It's important that the multimeter lead make contact right in the center of the positive battery post.
You may need two helpers for this test step, since someone will have to hold the RED multimeter lead onto the battery positive terminal and someone else will need to crank the vehicle while you perform the next step.
With the BLACK multimeter lead, touch the center of the starter solenoid Stud to which the big battery cable attaches to. You'll maintain the BLACK multimeter lead in this position throughout the next step.
Now, have a helper turn the key to crank the engine from inside the vehicle. This is important, since a voltage drop test has to be done while the component in question is working (or trying to work).
OK, if all is good (no voltage drop), your multimeter will register 0 Volts (.5 volts is still 0 Volts). If there's a voltage drop, your multimeter will register voltage (usually above 7 Volts DC.)
OK, now that the testing part is done... let's take a look at what your results mean:
CASE 1: Your multimeter registered 0 Volts (no voltage drop): This result indicates that the starter motor is receiving all of the battery voltage and Amperage it needs to crank the vehicle.
This also means that the starter motor is BAD, and here's why: In STARTER TEST 1 you confirmed that the starter motor is receiving the crank signal and in this test step you have confirmed that no voltage drop exists on the battery positive cable. These two results, taken together, indicate that the starter motor is BAD. Replacing the starter motor should solve your ‘No Crank Condition’.
I'm going to make two more recommendations to you. 1.) Before removing the starter motor, manually turn the engine using a 1/2 ratchet and the appropriate socket.. just to make sure the engine or the A/C compressor have not locked up and causing the No Crank Condition and 2.) Bench Test the starter motor after removing it. This is a super easy test to do and you can find this article by clicking here: How To Bench Test A Starter Motor (Step by Step) (at: easyautodiagnostics.com).
CASE 2: Your multimeter registered 5 Volts or more: This result tells you that a voltage drop does exist and this is not a good result.
The good news is that this can easily be corrected, since a voltage drop is always caused by some sort of corrosion issue on the battery positive cable or terminals or the battery positive post.
The solution is to thoroughly clean the battery positive post and the battery positive terminal (both the end that attaches to the battery positive post and the end the connects to the starter motor solenoid).
After cleaning, try cranking the engine. If it cranks and starts, no further testing is required.