GTV-6 fuel pump not running- volts escaping

[Jonathan Coates <cdico.demon.co.uk@cdico.demon.co.uk>]

In message , Chris Lesher <chris.lesher@cusys.edu> writes
>Now here's the wierd part that I could never figure out and hopefully some
>of the electrically knowledgeable folks can help out.  On my car I tested
>the p/w wire at the fuel pump and got a zero volts reading.  When I
>disconnected the p/w wire from the pump it read 10.6 volts.  This test was
>repeated many times.  What I finally did was bypass the p/w wire completely
>from combo relay to fuel pump and that wire showed 12+ volts - not to
>mention the pump now ran.  Why would the 10.6 volts get 'lost'?  does the
>pump not run without a full 12v?  and does the voltage going into the pump
>not go to ground unless the pump runs?
Chris, the reason the voltage dissapears when you connect the load is
due to the resistance of the wiring. This is showing you a fault and is
a really good clue. The voltage measured across any electrical item
(oops, nearly said thingy, or dooda) is proportional to it's resistance
and the amount of current flowing through it. Its the same for lamps,
motors, anything. Even wires, so if you connect your fuel pump and the
voltage across it dissappears, then there is a bigger voltage drop,
across a bigger resistance somewhere in your wiring. Find it, fix it and
you're there.
The voltage will turn up, and be measurable somewhere in the wiring.
Find both ends of the wire, and with the fuel pump hooked up you will
have a voltage (10.6 in your case, hey thats low anyway, another clue,
wire blocked, no volts getting through?) between one end of the wire and
the other. Follow the wire back and check the voltage between one end
and your test point. When you get virtually no volts, you are past the
fault. Leave the test prod which you have been moving where it is, at
the end of the good wiring. Now with the other prod, which you had left
at the end, start at the other end, where you started before to measure
voltage. You will initially get 10.6V (-10.6V to be exact, but I am
assuming DVM) and now you have a prod either side of the fault, or
faults. Move the prod at the end of the wire towards the other prod and
so long as you get the voltage reading you are spanning the fault. By
reducing the distance between the prods you can home in on the fault. It
can be a long tedious process, but so is pushing a car.
Remember that the volts appear across a resistance. If thats a bulb or
motor, then its good. If its supposed to be a wire, then its bad.
HTH
-- 
Jonathan Coates
164LV6 Daily driver
752.0TS T car
Alfetta 2.0 GTV Veni Vidi Visa
Manchester, nowhere near Barnsley, UK