TEST 2: Verifying The 12 Volt Start Signal
If you've reached this point, you've confirmed that applying 12 Volts directly to the solenoid (S terminal) engages the starter motor and cranks the engine.
Now we want to see if the starter is getting a 12 Volt signal (to crank the engine) from the ignition switch (when you turn the key to crank and start the engine).
Verifying this signal is pretty easy to perform and all you'll need is a multimeter to measure the voltage at the S terminal.
I want to point out that the 12 Volts should ONLY be present at the S terminal when you turn the key to the "START" position.
NOTE: You can perform this test with the S wire connected or disconnected to the S terminal.
These are the test steps:
- 1
Raise and place the front of the vehicle on jack stands (if it isn't already).
- 2
Place your multimeter in Volts DC mode.
- 3
Ground the black multimeter test lead directly on the negative (-) battery terminal using a jump start cable.
You can also Ground it on the engine, if you can find a clean, unpainted and rust-free spot of metal. - 4
Connect the red multimeter test lead to the S terminal wire using an appropriate tool.
Don't know which wire is the S terminal wire? It's the one that connects to the smaller of the three studs on the starter motor solenoid.
The S terminal wire (circuit) is the one that delivers the Start (Crank) signal from the ignition switch. - 5
Have your helper turn the key to crank the engine when the test is setup.
- 6
Your multimeter should read 10 to 12 Volts DC.
OK, let's take a look at your test result:
CASE 1: The wire is delivering 10 to 12 Volts when you turn the key to crank the engine. This is the correct test result and confirms that the starter motor is receiving an activation signal.
Your next and final test is: TEST 3: Voltage Drop Testing The Battery (+) Cable.
CASE 2: The wire IS NOT delivering 10 to 12 Volts when you turn the key to crank the engine. This test result confirms the starter motor isn't receiving an activation signal. Without it, the starter motor won't activate and crank the engine.
The missing starter motor activation signal is most likely caused by one of the following issues:
- A bad starter motor relay.
- A bad park-neutral safety switch (automatic transmission).
- A bad clutch pedal switch (manual transmission).
- A bad ignition switch.
- An anti-theft system fault (if equipped).
Although it's beyond the scope of this tutorial, your next step is to find the cause of the missing activation signal and resolve the issue.
TEST 3: Voltage Drop Testing The Battery (+) Cable
The starter motor needs a big surge of electricity to crank the engine. This large current comes directly from your pickup's battery.
The cable carrying this high current from the battery to the starter motor is the thickest cable connected to the starter and connects to the large stud that I've labeled 'BAT +' on the starter solenoid.
Unfortunately, this cable is prone to developing corrosion at its connection points, where the cable connects to the battery and starter. Sometimes this corrosion is easy to see as a white, green, or blue crusty buildup. However, some corrosion can be hidden within the connection itself.
No matter how much corrosion is present, it'll create resistance in the cable and reduce the voltage reaching the starter motor. This type of issue is called a voltage drop.
To check if a voltage drop on the cable is causing the starter motor failure, we can use a multimeter to perform a voltage drop test on it and that'll be the focus of this test section.
These are the test steps:
- 1
Place your multimeter in Volts DC mode.
- 2
Attach the red multimeter test lead to the positive (+) battery post. The positive (+) battery post must be clean and corrosion-free.
You may need two helpers for this test step, since someone will have to hold the red multimeter test lead onto the battery positive (+) post and someone else inside the vehicle (to crank it when everything is set up). - 3
Place the black multimeter test lead on the starter motor solenoid stud that connects to the battery positive (+) cable (see illustration above).
The orange arrow labeled with the "BAT +", in the illustration above, points to this stud.
Maintain the black multimeter test lead in this position throughout the next step. - 4
When everything is ready, have your helper turn the key to crank the engine.
Although the starter motor won't crank the engine, your helper has to turn the ignition switch to start the engine for the voltage drop test to work. - 5
The multimeter should register 0.5 Volts or less (0.5 V = 0 Volts).
If there's a problem in the wire, your multimeter will register some voltage, usually 5 Volts or more.
Let's interpret your test result:
CASE 1: Your multimeter indicated NO voltage drop (0.5 Volts or less). This is the correct test result, and it confirms the starter motor is receiving all of the battery voltage and amperage it needs to crank the engine.
You can conclude that the starter motor is bad and needs replacement if you have:
- Confirmed that the starter motor does not crank the engine when you directly apply 12 Volts to the starter's S terminal (TEST 1).
- Confirmed, in this test section, that the battery positive (+) cable does not have a voltage drop issue.
Now, before you remove the starter motor, do two more important things:
- Confirm the starter motor is receiving an activation signal (if you haven't already). TEST 2 will help you with this.
- Check that the engine is NOT mechanically locked up by manually turning it via its crankshaft pulley bolt (using a 1/2" ratchet and the appropriate size socket).
If you'd like to bench-test the starter motor (after removing it). You can find the step-by-step instructions here:
CASE 2: Your multimeter registered 5 Volts or more. This result confirms that the starter's battery (+) cable has corrosion on one or both terminal ends.
The issue causing the voltage drop in the cable will prevent the battery's total amperage output from reaching the starter motor.
Your next step is thoroughly cleaning both ends of the battery positive (+) cable with a small piece of sandpaper.
Eliminating the cause of the voltage drop should get the starter motor to crank the engine.
More 4.6L, 5.4L Ford F150, F250, And F350 Tutorials
There are quite a few 4.6L, 5.4L V8 F-Series pickup 'how to' tutorials and wiring diagrams you can find here:
F-Series Vans: You can find all of the available tutorials and wiring diagrams for the 4.6L and 5.4L V8 F-Series vans in this index:
- 4.6L, 5.4L Ford F150, E250, And E350 Index of Articles (at: troubleshootmyvehicle.com).
Crown Vic/Grand Marquis: You can find all of the available tutorials and wiring diagrams for the 4.6L V8 Ford Crown Vic and Mercury Grand Marquis in this index:
- 4.6L Crown Victoria And Grand Marquis Index of Articles (at: troubleshootmyvehicle.com).
If this info saved the day, buy me a beer!
