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Good idea to wire fuel pump this way?

11979 Views 16 Replies 6 Participants Last post by  Coppertop
Before i started rewiring my car, the power feed for the electric fuel pump was crimped into the battery cable where it connected to the post. Could i just wire it to the ACC terminal on the fuse box? If i did it this way would the fuel pump turn on when i start the car and turn off when i turn the car off? And would it get the 12V it needs? Thanx for any help.


1970 Camaro Z28
396/auto/posiMy 70 Z28
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Use a relay!!!

Connect the #85 of the relay to a good ground. Connect the #86 terminal on the relay to a lenght of wire. Have this wire enter the passenger compartment and hook it to the IGN terminal on the fuse box.

#30 needs to go to the battery (+), and for goodness sake use the correct size of wire and a fuse. Put the fuse close to the battery.

#87 goes to the fuel pump (+) wire itself.

The (-) wire of the fuel pump needs to go to a GOOD ground or directly to the battery (-).

Now when you start/run your car, the IGN terminal is live with 12 volts, causing the relay's coil to get energized, thus connecting #30 and #87 together (completing the circuit) for the pump's (+)12 volt supply.

Good luck!

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In an auto parts store, go to the lighting and accessories section. You'll find relays there even if they are labeled for "baja racing lighting"

First off, I highly discourage connecting aftermarket equipment to a 30 year old fuse box. Even if the wiring is new, the ACC (which is the incorrect terminal to use in the first place) can only handle about 10 amps MAX before the fuse blows. The average minimum draw of a fuel pump is about 7.5 amps, damn near 10, and just think, that 7.5 amps has to go thru a looooong set of wires before it reaches the battery.

I used 7.5 amps as an example. What does your fuel pump draw???? You should have this info somewhere, either on the pump itself, or in the instructions.

12 ga. wire can handle about 30 amps absolute maximum. I'd use 12 ga. wire for your application--but that depends on the length of the wire run too. Maybe someone else can chime in as I haven't found a reliable source on wire sizes to use for amprage draw. Your fuse would have to be big enough to handle the load, but not so big that it would allow too much current to go thru the wiring in case of a disaster.

In other words..
Let's say the pump draws 7.5 amps. If you used a 7.5 amp fuse, it would blow right away or not long after. Using a 40 amp fuse means that fuse would allow 40 amps to go thru the wiring and pump before it would blow--a disaster waiting to happen. 10 amps is what I would go with in that situation. Enough to let the nominal current thru, but low enough rating to prevent a disaster.

Hope that helps.

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You've got some good points on the ACC idea of being on, and the toggle idea of a big no-no....

But, if I understand your diagram right, that's NOT a good way at all to wire a fuel pump.

The oil pressure sensor is GROUNDED when the engine is NOT RUNNING. When the engine starts up, oil pressure from the pump builds up and pushes against the sensor, this UNGROUNDS it causing the idiot light to go off since the other side of the oil idiot light is always HOT with 12 volts when the key is in the ON/RUN/START position.

So you'd loose your negative connection when the engine is running normally. Besides, that sensor wire is NOT meant to carry the current demands of a fuel pump!


Wow, that little sucker doesn't draw much! So you wouldn't need the 12 ga., that would be over-kill. I'll have to get back to on the new wire size to use. At work I'm gonna photo copy a confusing chart that has wire lenght, amps drawn, wire gauge break-downs. I'll try to convert to "human" so I can help others on deciding what guage to use

14 ga. sounds about right. How close is this pump going to be mounted with respect to the battery?

Always remember it's okay to over-engineer something, I do this quite often. It's better to have a ridiculously large wire than a tiny wire on fire!

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That is quite a distance. In fact, I think I would stay with the 12 guage at least. Like I said, I'll have to get back to you for sure.


No offense taken

Thank you for clearing up 69_Malibu's post. That's makes sense. Yes, I thought he meant the oil sender switch.

That is a good point. If you wanted this safety switch, I would connect the ground of the relay #85 to one side of the pressure sensor switch, the other side of the switch goes to a convenient ground. That way when the oil pressure drops, the relay loses it's ground, and turns off, and of course turns off the fuel pump.
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12 ga. should do. (10 ga. if your kinda of safety freak like yours truly, but you might have trouble finding 10 ga. in that length from an auto parts store.) So run 12 ga. to the #30 on the relay from the battery with a fuse on it, and 12 ga. from #87 on the relay all the way back to the fuel pump. Make sure that fuel pump has a GOOD sheetmetal ground. I wouldn't recommend the frame itself.
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