electrical question: Ground problem?

[Marchalis]

Hi,
I have a car fuel pump no start problem.

test 1
The fuel pump in the yaris gets its negative/ground from the back of the cars body, and the positive goes to the dash. In this configuration the car won't start despite getting 12v through on startup from the plug attached to the fuel pump.


test 2
The fuel pump works with direct connection to a battery, negative and positive Direct from battery. proper pressure.


test 3
While Directly connecting the 'positive fuel pump wire', to the battery. but still drawing negative from the car body as usual, also no start, fuel pump doesn't pump. Zero fuel pressure.


test 4
negative/Ground from the back of the car is producing 12 volts,
Testing for spark from the negative/ground from the back of the car to the positive battery terminal, suggest that it's getting enough amps but I feel dubious about the assessment there. (I have no way really of testing for amps

I'm suspecting a ground problem but I might be missing something?



Cheers for any clues

[invalid username]

I don't know very much about the yaris, but on my 1995 4runner there are some things that receive 12v all the time, and the ground wire is switched. Just a thought.

[Marchalis]

:Solved:


Lack of sleep over problem was the cause?


When I tested the fuel pump I tested the negative and positive as indicated on the pump.

It was a new pump that looked identical to the old. The plug that went into the pump only fit one way.

I can't say if I installed the pump with the plug somehow back to front or if the motor came in reverse, but changing the negative and positive on the top of the fuel pump unit in the car fixed the problem.

With direct connection the pump will make noise and run in reverse, but connected to the car it will not.