TEST 3: Testing The Starter Motor Relay's Activation Signal
The starter motor relay is the component that sends the 'Start' signal to the starter motor solenoid's S terminal.
For this to happen, the starter motor relay has to receive its own activation signal.
So in this section, we'll make sure that the starter motor relay receives this activation signal.
LOCATION: The location of the starter motor relay is in the right front corner of the engine compartment, near the battery.
These are the test steps:
Disconnect the red with light blue stripe (RED/LT BLU) wire from the starter motor relay.
The orange arrow in the photos above points to the RED/LT BLU wire.
Place your multimeter in Volts DC mode.
Connect the black multimeter test lead to the battery negative (-) post.
Connect the red multimeter test lead to the RED/LT BLU wire you just disconnected from the starter motor relay.
Have your helper turn the key to start the engine.
Your multimeter should register 10 to 12 Volts DC.
Let's take a look at what your results mean:
CASE 1: The multimeter registered 10 to 12 Volts DC. This is the correct and expected test result and it lets you know that the starter motor relay is receiving an activation signal.
You can conclude that the starter motor relay is bad (and needs to be replaced) if you have:
- Confirmed that the starter motor does crank the engine when you directly apply 12 Volts to the starter motor solenoid's S terminal (TEST 1).
- Confirmed that the starter motor solenoid's S terminal wire IS NOT delivering a 12 V 'Start' signal (TEST 2).
CASE 2: The multimeter DID NOT register 10 to 12 Volts DC. This test result tells you that the starter motor relay is not receiving an activation signal. Without it, the starter motor relay won't send a 'Start' signal to the starter motor.
The most likely causes of this missing starter motor relay activation signal is:
- A misadjusted park/neutral safety switch.
- Fuse 7 of the interior fuse box is blown (1994-1996 only).
- A bad ignition switch.
Your next step is to test the park/neutral safety switch, check fuse 7 (1994-1996 only), and test the ignition switch.
TEST 4: Voltage Drop Testing The BAT (+) Cable
In this test section we're gonna' find out if the starter motor is receiving the total amount of amperage it needs to crank the engine.
We'll accomplish this by doing a simple multimeter voltage drop test on the battery positive (+) cable.
Let's get going:
Place your multimeter in Volts DC mode.
Connect the red multimeter test lead on the center of the battery positive post.
NOTE: The battery must remain connected to both its cables.
Connect the black multimeter test lead to the stater motor solenoid's stud that connects to the battery positive (+) cable.
The orange arrow labeled with BAT (+) in the photo above points to this stud.
Maintain the black multimeter test lead in this position throughout the next step.
When everything is ready, have your helper 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.
While your helper is trying to crank the engine the multimeter should register 0.5 Volts or less (0.5 V is really 0 Volts).
If there's a problem in this circuit, your multimeter will register some voltage, usually 5 Volts or above.
OK, let's take a look at what your results mean:
CASE 1: Your multimeter indicated NO voltage drop (0.5 Volts or less). This is the correct and expected test result and it confirms that the starter motor is getting the full amount of voltage and amperage the battery can deliver.
You can conclude that the starter motor is bad and needs to be replaced if:
- The starter motor does not crank the engine when you applied 12 Volts to the starter motor solenoid's S terminal (TEST 1).
- The starter motor solenoid's S terminal is receiving 10 to 12 Volts (TEST 2).
- There's no voltage drop in the circuit (wires) that connect the starter motor solenoid BAT (+) terminal to the battery's positive (+) post.
Now before you remove the starter motor, do one more thing: Turn the engine manually (using a 1/2 ratchet and the appropriate socket). This will verify that the engine is not mechanically locked up.
CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and that it's keeping the full amount of amperage the battery can provide from reaching the starter motor.
The solution is to:
- Disconnect both battery cables from the battery and thoroughly clean their terminals.
- Disconnect the cables at the starter motor relay and clean their round terminals.
- Disconnect the cable that's attached to the starter motor solenoid's BAT (+) terminal and clean its round metal terminal.
Cleaning the cables' round terminals should be done with a small piece of sand paper. Once all cable terminals are clean, reconnect everything and try cranking the engine. If the voltage drop was the cause of the no-crank condition, the engine will now crank and start.
More Ford E150, E250, and E350 Tutorials
You can find a complete list of tutorials for the full-size Ford E-Series vans here: Ford 4.9L, 5.0L, 5.9L Index Of Articles.
Here's a small sample of the tutorials you'll find:
- Manifold Absolute Pressure MAP Sensor Test (Ford 4.9L, 5.0L, 5.8L).
- Ignition Coil Test -No Spark No Start Tests (Ford 4.9L, 5.0L, 5.8L).
- How To Troubleshoot A No Start (Ford 4.9L, 5.0L, 5.8L).
- Testing A Blown Head Gasket (Ford 4.9L, 5.0L, 5.8L).
- How To Test Engine Compression (4.9L, 5.0L, 5.8L).
If this info saved the day, buy me a beer!