Testing The Ford EEC Power Relay (Brown Relay)

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:
   1. 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.
   1. You can back probe the EEC Power Relay connector.
   2. Or pierce the wire with a wire piercing probe (to see an example of this, click here: Wire Piercing Probe).
   3. 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:
   1. Battery voltage (10 to 12 Volts DC).
   2. 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.

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.

TEST 2: Checking For Power (High Current Circuit)

In this test step, we're gonna' check that the wire that supplies power (10 to 12 Volts DC) to the EEC Power Relay's high current circuit is actually providing this juice.

The wire that provides this juice is the wire labeled with the number 4.

As before, in TEST 1, you can check for this voltage with the EEC Power Relay connected to its connector or not.

OK, to get this test going, this is what you'll need to do:

1. Place your multimeter in Volts DC mode.
2. With the red multimeter test lead, probe the wire labeled with the number 4.
   1. This is where a wire piercing probe comes in handy (to see what this tool looks like, click here: Wire Piercing Probe).
   2. NOTE: Avoid probing the front of the EEC Power Relay connector with the multimeter lead (yes, I know, it's the easiest way to go about checking this circuit), but the metal female terminal could get damaged and this is a nightmare you don't need or want.
3. Ground the black multimeter test lead directly on the battery negative terminal or on a clean metal spot on the engine.
4. Your multimeter should register one of two things:
   1. Battery voltage (10 to 12 Volts DC).
   2. Or no voltage at all.
   NOTE: Voltage should be present at all times (whether the Key is On or not).

OK, let's interpret your test results:

CASE 1: Your multimeter showed battery power. This is the normal and expected test result.

We now know that the high current circuit of the EEC Power Relay is being fed power.

The next step is to check/confirm that the EEC Power Relay is sending voltage out from the wire labeled with the number 3. Go to: TEST 3: Testing The EEC Power Relay Voltage Output.

CASE 2: Your multimeter DID NOT show battery power. Recheck all of your multimeter connections and repeat the test one more time

If the multimeter still does not 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.

These 10 to 12 Volts are provided by an inline fusible link (on the starter motor solenoid) or by a mega fuse on the engine compartment fuse box.

The most common cause of this missing voltage will be that the inline fusible link or the mega fuse is blown.