Your volts go up because there aren't any other devices leaching current from the fuel pump feed. Checking voltage with a dedicated line to the pump means you aren't getting other devices leaching current, dropping voltage. Battery to pump has nothing hooked to it when checking voltage (breaking the only circuit on the line). You're seeing exactly what the pump sees before current leaks into it. Also some of it is larger wire has less resistance to a degree, but more of it is leaking current. A 20ga wire would also show 14 or 15v. Current leak + smaller wire + other shit taking from a hot line = drop in voltage and available current.
Unless I am misunderstanding your post:
I don't think you understand how voltage drops work if you think that feeding a fuel pump with a 20 ga wire 15 feet long will not yeild a lower voltage at the pump. There most certainly will a voltage drop across the wire because of internal resistance and the amount of current draw from he pump itself.
E = I * R applies very well for what we are talking about here. A wire with no current flowing though it will have no voltage drop.
We can go into more detail if needed.
IF you check the voltage at the pump
WITH IT RUNNING, then you are in fact seeing the effects of running a dedicated larger diameter wire.
With that said, the point about the chassis being a piss poor conductor is totally relevant. If you want to see how shitty it is, then put the maximum load that you can on your electrical system and perform a voltage drop test between you fuel pump's negative terminal and the negative battery terminal. Hell, just look at the pathetic ground straps and ground connections from the factory.
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Topic: Fuel pump rewire (Read 5793 times)