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The first connection is at the postitive terminal
of the battery, which, in my car, reads about 13.5V
when the car is running.
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Starting in the upper left corner of the diagram, battery
voltage is run from the positive terminal of the battery
through various fuses and junction blocks, where it arrives
at pin #7 - (B)lack wire with (W)hite stripe - of the MFI relay.
In my car, the voltage at pin #7 of the MFI relay is about
12.5V when the car is running.
The MFI relay is the big
gold-colored box on the passenger's side of the center console
near the radio (under the carpeted trim piece). The MFI
relay's 8-wire harness is labeled C-44 in the service
manual and the pinout diagram is printed above for your
convenience.
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The MFI relay's coil is controlled by the ECU - when the
ECU's output falls to 0V (ground), the relay energizes and
MFI relay pin #1 is internally connected to MFI relay pin #7. The ECU
turns on the MFI relay whenever the ignition is turned to
the "Start" position and whenever the engine is
running.
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When MFI relay pins #1 and #7 are connected, then power is
applied to pin #1 of the MFI relay, which is a (B)lack wire
with a (L)ight blue stripe.
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The fuel pump relay gets its power from the output of the
MFI relay, where pin #1 of the MFI relay harness is connected
to pin #3 (and pin #5) of the fuel pump relay. The fuel pump relay
is located on the underside of the fuse box bracket to the
rear of the passenger's side headlight.
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The ECU controls the fuel pump relay via pin #1 on the
fuel pump relay harness, which is connected to ECU pin #31
via a (B)lack wire with a (R)ed stripe. When this wire
is grounded by the ECU (0.0V) then fuel pump relay pins
#4 and #5 are connected. Normally (when the ECU is not
grounding pin #1 of the fuel pump relay), pin #5 is
internally connected to pin #2 of the fuel pump relay.
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If the fuel pump relay is off (pin #1 is NOT grounded),
then pin #5 is connected to pin #2. This means that
(B)lack wire with the (L)ight blue stripe connected to
pin #2 of the fuel pump relay is receiving power. Since
that same wire runs all the way back to your fuel pump
in the trunk, the fuel pump receives power at pin #3 of the
fuel pump harness, and fuel flows into the high-pressure
fuel lines.
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If the fuel pump relay is on (pin #1 IS grounded),
then pin #5 is connected to pin #4. This means that
(L)ight blue wire with the (B)lack stripe connected to
pin #1 of the fuel pump power resistor receives power.
The resistor's purpose is to cause the voltage "seen"
by the pump to be less than normal (approximately 8.5V).
The output of the resistor (pin #2) is connected to
the input of the fuel pump (pin #3 on the pump harness).
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