[Wanna_Chev]

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.

Jeff

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1970 Camaro Z28
396/auto/posiMy 70 Z28

 

[d1_bradley]

That would work. A lot of guys "hide" a switch under the dash or seat or somewhere that also needs to be on for the pump to run. A poor mans anti-theft device. It won't go too far with just the carb fuel. Just wire it in series with the "hot" wire to the pump.

 

[Wanna_Chev]

I actually had a switch, but i fried it. Plus it was kind of a pita, for me anyways. thanx for the response.

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1970 Camaro Z28
396/auto/posi My 70 Z28

 

[ddhughe]

Go to www.painlesswiring.com and read about relays, you should definitely have one in your fuel pump circuit.

 

[Coppertop]

NO

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!

Joe

 

[Wanna_Chev]

Ooooooooook......

What size of wire should i use and what kind of fuse? Can i get a relay at a hardware or auto parts store? Thanx for the help.

BTW, what would happen if i wired it as mentioned in my 1st post?

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1970 Camaro Z28
396/auto/posi

My 70 Z28

[This message has been edited by Wanna_Chev (edited 08-16-2000).]

 

[Coppertop]

Jeff,

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.

Joe

 

[Wanna_Chev]

Excellent, thanx God, er...i mean Joe.

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1970 Camaro Z28
396/auto/posi
My 70 Z28

 

[69_Malibu]

another good method, which i think is the safest is:

acc(+)-----oil pressure switch-------fuel pump----(-)


if you simply wire it to acc then you will be pumping gas when the key is turned--even if your car is not running!!! with this method the car has to be turned on AND running. in CA it is illegal to have a toggle switch controlling your fuel pump...if you get in an accident, who's gonna turn it off???

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69 Chevelle Malibu
My Chevelle

 

[Coppertop]

69_Malibu,

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!

Joe

 

[Wanna_Chev]

Joe, i found out it's a 4.5 amp fuel pump. Would this help out in deciding what guage of wire to use from the battery to the relay? Thanx for the help.

Jeff

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1970 Camaro Z28
396/auto/posi
My 70 Z28

 

[Coppertop]

Jeff,

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!

Joe

 

[Wanna_Chev]

Thanx Joe. It's mounted right above the gas tank, so it's a good distance from the battery. I'm almost finished rewiring my harness for the guages, just have the ammeter prob. I hope to god it works or i'll be walking to school again

. Thanx.

------------------
1970 Camaro Z28
396/auto/posi
My 70 Z28

 

[Coppertop]

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.

Joe

 

[BC]

Wanna,
I agree with 69_Malibu that you definitely need some other switch to automatically shut it off if you were to ever get in an accident. I don't believe it will pass tech inspection just wired to the acc terminal if that is of concern for you. I think Coppertop kinda missed to oil pressure switch idea (no offense) in that an oil pressure switch is different from the oil pressure sending unit. Please do not try to run the 12v through the oil pressure sending unit. An oil pressure switch is a separate unit that has two terminals that get shorted together when there is oil pressure, but are open when no pressure is present. The is a good idea so that in an accident and the ignition is still on, the fuel pump does not continue to spew gas everywhere. (Unless the engine stays running!) The only problem with the oil pressuse switch is actually plumbing into the motor somewhere where it can accurately read pressure. For your distance, I would definitely stay with 12g wire, especially with that many connections. Hope this helps.



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Bill C.
'71 SS (now with 468BBC)
ACES #2780
Colo Spgs, CO

 

[Coppertop]

Bill,

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.

 

[Coppertop]

Jeff,

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.