How can an in-tank fuel pump be wired wrong?

I just want to be sure I am not missing something, because I did hard-
wire a 1988 model unit onto a 1987 car, and they units are different,
but the wires are the same.

I tested the wires on the unit with an ohmmeter to make sure I knew
what sent current where.

My results are that the purple wire goes to the pump, the black wire
from the pump grounds to the unit and that grounds to the chassis.

The brown and gray/white wires go to the gauge on the sending unit.

So, I connect the black wire as a ground to the chassis. There are
three remaining wires:

1- brown from the sending unit goes to brown from the car.
2- gray/white from the sending unit goes to gray/white from the car
3- the remaining wire, I think purple, goes to the remaining wire from
the car - I think purple also.

How could a pump get reversed with only 1 wire connecting it?

Thanks!

Jamie

 

My suggestion would be to get a new pump designed for that car. Why
fiddle around trying to make a component designed for another car,
work in your car?

 

Wiring diagram in the '87 green book reads, "pink to pink (maybe purple with
age), brown to brown and gray/white to gray/white. Power to the gauge comes
to the sending unit from the instrument panel via the gray/white wire and
the brown connects to the sending unit resistor(rheostat) wiper arm to
chassis ground and regulates current thru the resistor and the fuel gauge,
thus changing the gauge reading, based on the position of the sending unit
float.. The pink(now purple?) supplies power to the in tank fuel pump.

Fuse 1 protects the power applied thru the fuel injection relay to ECU and
also to the in tank pump, but fuse 11 also protects the in tank pump on the
pump side of the fuel injection relay. If the fuel injection relay is
engaging, F11, according to the '87 Volvo green book, could be blown and no
power would reach the in tank fuel pump. An easy test is with a voltmeter or
a 12 volt bulb with pigtail wires soldered, one to the center of the base of
the bulb and the other to the metal bulb base. Or just buy a bulb socket
with pigtail wires at your friendly parts house.Test the bulb and
wiring/soldering by touching one of the wires end to the positive battery
terminal and the other wire end to the negative battery terminal. After
confirming the bulb will illuminate, turn on the ignition switch and connect
one of the leads(wires) to a convenient chassis ground point. Any convenient
screw/bolt that is attached to the car body will do. Insert a straight pin
thru the pink(purple) wire to the in tank pump and touch the other wire from
the test bulb to the pin. the bulb should illuminate indicating power to the
pump.