6.5 volts does not sound right. With the test lead jumped to the battery you should get battery voltage back to the stock connector. You could also have a bad ground connection. To the pump. If the ground is ok and you have 12 volts on the correct wire to the pump then the pump is defective.
racetronix fuel pump and hot wire kit
- Thread starter Robert Dean
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Robert Dean
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- Jul 13, 2015
I don't understand why the low voltage at the factory harness but the full voltage at the hotwire harness. There's still power going through the factory harness no matter what. But why the increase when going through the hotwire harness? Could the factory relay be fried? How do I check for ground connection, good or bad, at the pump?
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- Nov 30, 2009
When you tested for 12v back at the connector did you put one test lead to chassis ground or did you put both test ( meter ) leads to the connector ? If you have 6.5v with one lead on the connector and one to chassis , your wiring from the relay under the hood is bad . If you have 12v you have a bad ground anywhere from tank to chassis . Your hotwire kit brings 12v straight from the back of the alternator through a 30a fuse to the hotwire relay . The hotwire relay is "turned on " by the factory fuel pump wiring . More than likely you have a bad ground at the back , check them all . It wouldn't be a bad idea to run at least a 10 gauge wire from battery negative to the back near the hotwire relay to insure a good ground . Good luck , Sam
Robert Dean
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- Jul 13, 2015
No. I didn't use a chassis ground when I did the multimeter test. I put the leads of the meter onto to connector of the factory fuel pump harness at the back and I got 6.5 volts. I did the same after I plugged the hotwire harness into to factory harness at the back and tested the hotwire harness connector and got 12 volts. I have a big 8 gauge ground from battery negative to the inner fender near the battery. I don't think I have a ground problem, I'm getting 12 volts to the pump, no fuses are blowing anywhere.
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- Nov 30, 2009
You might have 12v to the pump , but that 12v has to go back to ground after going through the pump . So it's possible to have 12v at the pump but it can't make it back to ground ( a complete circuit ) . No fuses will blow without a complete circuit to ground . Try this , hook everything back up just the way it was when it died . Put the fuel pump jumper in under the hood . Next go to the back and remove the hot wire relay then lightly plug it back in . Did you hear or feel it click ? If not you are not energizing the hotwire relay , so now unplug the factory harness from the hotwire connector . check with meter for 12v to chassis in the factory harness . If you have 12v checking that way , you have a bad ground .
Robert Dean
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- Jul 13, 2015
Ok, so here's what happened. I put the fuel pump jumper in under the hood, went to the back and unplugged the factory harness from the hotwire and plugged it back in lightly. It does trigger the relay, I can here it click, so it is energizing the the hotwire. So then I left the jumper connected and tested the factory harness to chassis ground and I am getting 12 volts with a multimeter. Does that mean I have a bad ground somewhere in the factory wiring or is it supposed to show 12 volts?
Robert Dean
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- Jul 13, 2015
Strange thing is that when i test the factory harness at the back with a multimeter not using a chassis ground, just touching the multimeter leads on the contacts on the harness it shows 6.5 volts. But when I plug it into the hotwire harness and test the contacts coming out of the hotwire, again, not using chassis ground, just touching the multimeter leads to the contacts on the harness it shows 12 volts. Is this normal? Do I have a problem with factory wiring? Or is the fuel defective? It's also strange that I had the car running after I installed everything and it was perfect. Everything was working perfectly, it sounded great, then I just stopped because the fuel pump stopped working. If there was a bad ground somewhere, why would it work at all in the first place for 20 minutes? (which is how long the car was running for before the pump stopped)
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- Nov 30, 2009
Yes , the factory harness has a separate ground path than the output of the hotwire . The hotwire circuit is completely separate form the factory harness except for the factory harness pulls in the hot wire relay . 12v connector to chassis & 6.5v connector to connector tells me bad ground in factory harness . 6.5v may be enough to pull in the hotwire relay but I wouldn't rely on it . If the hotwire relay pulled in and you have 12v going up to the pump , it's time to drop the tank and check connections at the top of the tank . The yellow bulk head connector on the sending unit is known for burning up and causing the pump to not turn on ( I had this problem on 3 separate cars ). Also in-tank wiring and lastly the pump . Be thankful that it died in the garage and not on the road . I use to get that all the time when I fixed TV's back in the 70's ...... " It was working fine yesterday " ...... "Well it's broke now!!". You should be able to break into the factory harness ground wire and run another straight to the chassis .
Robert Dean
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- Jul 13, 2015
So can I break into the factory harness ground wire at the back close to where it plugs into hotwire harness and go straight to chassis ground from there?
Robert Dean
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- Jul 13, 2015
I changed that yellow bulk head connector on the top of the tank when I put the hotwire kit and new pump in. It's a better piece than the original factory connector (according to racetronix). They recommended it when I ordered the hotwire kit. But ya, I definitely have 12 volts coming out of the hotwire harness.
Robert Dean
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- Jul 13, 2015
So I probably have an in tank wiring problem or a defective fuel pump.
Robert Dean
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- Jul 13, 2015
I have a question. I thought maybe the factory fuel pump relay up at the front on the fender might be wacky so I unplugged the relay, identified power and ground wires and made a jumper wire to go between them. I hooked up the fuel pump test wire near the alternator and the wire got hot. As in temperature hot. Is that a bad Idea to do that or does that mean something is grounding out somewhere?
Robert Dean
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- Jul 13, 2015
So here's an update. I did have a bad ground on the factory harness. But I found it and made the repair and now I'm getting the full 12 volts from the factory harness. And that's with test leads from the multimeter on the factory harness contacts. So I'm getting 12 volts from factory harness, 12 volts from hotwire harness. So the fuel pump should run but it doesn't. Defective fuel pump?
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- Nov 30, 2009
Bad idea ! That is a dead short to ground . But if you still have that bad ground at the back of the car , there was just enough resistance to not pop a fuse and get the wire hot . That would have popped the fuse after a little bit though , and proved that you have a bad ground in that circuit or it would have popped instantly .
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- Nov 30, 2009
I would drop the tank at this point and again check all connections and if they are good , change the pump .
I prefer to run a separate ground all the way to the engine or battery. I use a weatherpack connector and de-pin the hot wire connector and add the ground eliminating the poor factory ground path.
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- Nov 30, 2009
I agree, that is why I told him in my first post he should run a 10ga wire from the battery to the back. I like the weather pack idea.
