Testing The Ford EEC Power Relay (Brown Relay)

The EEC Power Relay not only supplies battery voltage to the fuel injection computer (also known as the E.E.C. Electronic Control Assembly), but also supplies power to the fuel injectors, the fuel pump relay, and a few other emissions related solenoids.

The EEC Power Relay is easy to recognize because it's usually a brown color. If the EEC Power Relay has already been replaced, you can still recognize it by its brown colored connector.

In this 'how to' tutorial, I'll show you how to test it on your Ford car or pickup in a step-by-step manner.

Just in case you've ever wondered what the heck the acronym E.E.C. stands for, it's: Electronic Engine Control.

You can find this tutorial in Spanish here: Cómo Probar El EEC Power Relay (Relé De La Computadora De La Inyección Electrónica) (at: autotecnico-online.com).

NOTE: For your cross reference information, this article will help you test the following EEC Power Relays:

1. AutoZone part #:
   • Duralast 19840
2. O'Reilly Auto Parts part #:
   • BWD R648
   • AC Delco F1777A
3. Others:
   • STANDARD MOTOR PRODUCTS Part # RY71T
   • STANDARD MOTOR PRODUCTS Part # RY71
   • WELLS Part # 19840

What Tools Do I Need To Test The Relay?

You need a few basic things to test the EEC Power Relay and they are:

1. Multimeter
   • A digital or analog multimeter will work.
   • If you need to buy one or are looking to upgrade, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
2. Wire Piercing Probe
   • This tool is a time saver of the first order. To see what this tool looks like, click here: Wire Piercing Probe.
3. Jumper Wires
   • You'll need two of them with alligator clips on both ends (you can make these yourself).

EEC Power Relay Circuit Descriptions

Each of the 4 circuits (wires) of the EEC Power Relay has a specific job to do and these job descriptions are:

IMPORTANT: Your specific Ford vehicle may not have the exact same colors listed below. This is no big deal, since the circuit descriptions are the same. You will be able to use the info in this article to diagnose the EEC Power Relay on your Ford vehicle even if the colors of the EEC Power Relay connector's wires are not the same!

EEC Power Relay Circuits
Pin	Wire Color	Description
1	Black *	Chassis Ground
2	White w/ Light Blue stripe *	Power (from ignition switch)
3	Red *	Voltage Output
4	Yellow *	Fused Power (hot all of the time)

  * Your specific Ford vehicle may have different colors.

Relay Basics: How The EEC Power Relay Works

In this section, I'm gonna' go into a little (and I stress 'little') working theory of the EEC Power Relay to better help you understand what it is that we're gonna' test in this tutorial.

Every Ford EEC Power Relay has two basic circuits and for the purpose of our discussion, we'll call them:

1. A low current circuit.
   • This circuit can be identified by the wires labeled with the numbers 1 and 2.
   • The low current circuit is the control circuit that 'closes' or 'opens' the high current circuit.
   • By 'closing' the high current circuit, I specifically mean allowing voltage to pass thru' the relay (internally) and on its way to the fuel injection computer, fuel injectors, fuel pump relay, etc.
2. A high current circuit.
   • This circuit can be identified by the wires labeled with the numbers 3 and 4.
   • This is the circuit that delivers the voltage (and thus current) to the fuel injection computer (EEC Electronic Control Assembly), fuel injectors, fuel pump relay, etc.
   • When the relay is not activated, this circuit is 'open', and as such, does not send any power to anything.

Both of these circuits are completely independent from one another, since the voltage/current flowing thru' them don't mix.

To get into more specifics, this is what happens when you turn On the Key and crank the engine:

1. Power (in the form of 10 to 12 Volts) is applied to circuit 2.
   • This voltage comes from the ignition switch.
2. Power (in the form of 10 to 12 Volts) is always present in circuit 4.
   • This voltage comes directly from the battery positive (+) terminal across a fusible link on the starter motor solenoid (on the fender).
3. Ground is always present on circuit 1.
4. As soon as the ignition switch powers up circuit number 2, the EEC Power Relay closes circuit 3 to circuit 4.
   • This causes voltage to reach the fuel pump relay, the fuel injectors, the fuel injection computer, etc. to get power through circuit number 3.

As you can see it's nothing too complicated and testing the EEC Power Relay isn't complicated either and I'll show you how in the next couple of pages.

OK, working theory lesson is over, let's get testing in the next page.

Where To Buy The EEC Power Relay

You can find the EEC Power Relay here:

TEST 1: Checking For Power (Low Current Circuit)

If you read the section 'EEC Power Relay Circuit Descriptions', you're aware that there are 2 wires that supply power to the EEC Power Relay.

These two wires are labeled with the numbers 2 and 4..

Wire labeled with the number 2 feeds the low current circuit of the EEC Power Relay with 10 to 12 Volts from the ignition switch.

Circuit 4 feeds the high current circuit of the EEC Power Relay, but we'll check this in TEST 2.

In this test, we'll focus on testing wire number 2 first (this wire is the one that feeds power to the low current circuit).

You can perform this test with the EEC Power Relay connected to its connector or not. OK, this is what you'll need to do:

1. Locate the EEC Power Relay (in the engine compartment) and:
   • Remove the black electrical tape and expose the relay's wires.
2. Locate the wire that corresponds to circuit number 2.
3. With your multimeter in Volts DC mode probe the wire that corresponds to circuit 2.
   • You can back probe the EEC Power Relay connector.
   • Or pierce the wire with a wire piercing probe (to see an example of this, click here: Wire Piercing Probe).
   • NOTE: It's best NOT to probe the front of the EEC Power Relay's connector or you run the risk of damaging the metal female connector inside.
4. Ground the black multimeter test lead directly on the battery negative (-) terminal or on a clean metal spot on the engine.
5. Turn the Key On.
6. Your multimeter should register one of two things:
   • Battery voltage (10 to 12 Volts DC).
   • Or no voltage at all.
7. When done, turn the Key Off.

OK, let's interpret your test results:

CASE 1: Your multimeter registered 10 to 12 Volts DC. This is good and tells you that the ignition switch (via a fuse) is powering up the low current circuit of the EEC Power Relay.

The next step is to verify that the EEC Power Relay's high current circuit is being fed with battery power too. Go to: TEST 2: Checking For Power (High Current Circuit).

CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC. Double check that you're probing the right wire and repeat the test.

If the multimeter still doesn't register battery voltage (10 to 12 Volts DC) this second or third time around, then you need to find out why this voltage is missing.

Although diagnosing this missing voltage is beyond the scope of this article, I can tell you that the ignition switch is the one that provides this power thru' a fuse and this fuse is probably blown.