Fuel Pump Wiring/Electrical Input Needed

[Charles Young]

Here's the short story.
The car has a hot wire kit with 30A fuse and relay under the hood. Recently the car would not start...no fuel pressure. I unplugged the hotwire connector at the back of the car and reconnected what I beleive is the factory hot lead and the car runs fine. Checked out the HW relay and with the car running the relay has 14V on the output and 14V at the back of the car but when I plug the pump lead back into the hotwire connector (with 14V) it will not run the pump. Sounds like a ground maybe but the pump runs fine with factory wiring and changing nothing but which hot lead I plug into the pump wiring. Isn't the ground the same regardless of which 14V lead I plug into the pump? I don't get it. Any suggestions?
Thanks,
Charles

 

[pacecarta]

try another relay , if no good theres a wiring issue on the jumper plugs or at the relay
, check the contacts on the plugs and the relay socket for any corrosion or loose wireing to the contacts
if relay doesnt fix it and you cant see the issue in the jumper wiring just replace the HotWire setup

 

[Charles Young]

I have 14v at the back of the car on the hot wire connector. Doesn't that eliminate concerns with the relay?


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[pacecarta]

are you sure you're checking the fuel pump wire ... its not the red(pink) one ..thats for the fuel level sender

pump is at end of connector ,pin C ,tan wire

http://vortexbuicks-etc.com/fuel_pump.htm

 

[Charles Young]

I'm pretty sure but will check again tonight.


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[Nick Micale]

I have 14v at the back of the car on the hot wire connector. Doesn't that eliminate concerns with the relay?..........

This may not be the specific reason for your issue, but if you have a 10 ga. wire supplying power to the pump, that is only1/2 of the circuit which also must be a 10 ga. ground back to the battery or alternator.

Some people say the frame or body ground is ok, but as I have seen many pumps, wiring, relays and connectors fail which was attributed to a poor ground.

Please do not tell me that a 30 year old low carbon steel frame with many rusted joints, or the body itself, is as good a ground compared to a quality 10 ga. stranded copper wire over 20 feet?

 

[Charles Young]

Thanks for the input gentlemen! I'll report back.

 

[dynoman]

With factory harness working ok and have 14v at the hot wire connector going to the intermediate harness up to the pump and no pump running . The problem is in the hot wire ground circuit . Check those connections, then do like Nick said and run a 10ga ground back to the negative on the battery.

 

[Charles Young]

OK, dumb question....how/where is the pump motor grounded?

 

[davelostmissing]

You could put a resistor in series with that wire and still see 14v on an open circuit without load. Only when you load a wire/relay/circuit and still see good voltage have you absolutely confirmed it is good

 

[dynoman]

Use a test light , that will put a small load on the circuit , better than a DVM.

 

[Charles Young]

You could put a resistor in series with that wire and still see 14v on an open circuit without load. Only when you load a wire/relay/circuit have you absolutely confirmed it is good

Oh..didn't think about that. So the relay could even drop out with load on the circuit?

 

[davelostmissing]

Unfortunately bad relay contacts could behave like a resistor , show voltage but not pass appropriate current.. Corroded wires same.

 

[pacecarta]

..he said it runs fine on stock harness so no need to be looking at the pump ground
the fuel pump ground is soldered to the top of the sender hat and then through the oe pump connector under tail lamps and ends inside the trunk on the floor with a ground connector that clips into a square hole and also has a small screw to make a solid mechanical ground connection to the chassis

his issue seems to be in the jumper plugs or wiring between them for the hotwire ...or the relay or its wiring . most hotwires have the relay at the trunk and that relay gets its coil feed and coil ground through the oe pump harness . if its an early shitty (for lack of a better term) hotwire the relay could be under the hood and the coil feed for the relay iss off the fuel prime lead by the alternator and the ground for the relay usually went to the fender and he may have a cruddy ground connection there or a bad (cut) wire from the relay to the harness jumper by the trunk

 

[Charles Young]

It was the hot wire relay. Even though it was getting 12 v it wasn't holding. Thank you all for the help!!!


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