Need help with wiring electric fuel pump.

[Gould]

Hello. I've been a member here for years but since my Bronco project(s) got moved down my to-do list for many of those years I haven't been reading or posting. Hopefully I will be able to stay on top of this one for a while.

My problem right now is with a 1973 wagon with the 302 V8 and 3-speed manual. I mounted an electric fuel pump and it seems to work well; but since I didn't know any better I just ran the hot wire to the battery for testing it out.

Now that I know it works I would like to wire this a little better. I have seen a lot of talk about inertia switches and oil pressure switches in other posts as well as installing a "security" switch. All great ideas. And when I get around to redoing all the wiring I will likely implement some of them.

In the meantime I would like to just wire this pump in so that it only runs when the key is turned to "Run" or "Start" positions. Where, physically, is it best to make that connection? At the ignition switch? Somewhere else?

Looking at this wiring diagram from Seabiscuit (http://seabiscuit68.tripod.com/images/73-74_06-11_color.gif) it appears there is a thing called a "Constant Voltage Unit" that gets wired to the "Run" terminal of the ignition switch. Is this a good place to connect the electric fuel pump? Where do I find that physically on the truck?

Is there a fused circuit I could patch this into that would be a better choice?

The pump I installed is made by Airtex and the instructions simply say "Connect the pump power wire (+) to a power supply that is controlled by the ignition switch."

All help is appreciated. My plan is to do a rather thorough rebuild next year. I just need this running soon since it is my plow truck for the winter.

Thanks!
Gould

 

[75brnco]

I would probably tap into the ing switch with a fusable link, then into an inertia switch from a ford taurus or similar there a dime a dozen at pick n pull.

 

[John Marinan]

I have an on off toggle on the bottom of the dash behind the ac outlet. This is a cheap security system and makes it easy to cut off the pump when you're working on something else electrical. I have used a push in, off on, switch on another car. I put a nut on the end of it instead of the knob so it looks and feels like just another bolt under the dash.

 

[707Bronk]

You could wire it onto one of the posts of the starter solenoid. One of them will provide power when ignition switch is set to "run". You should wire in a automatic reset breaker inline as well. You could use a fusible link, fuse or manual reset breaker as well. I am just not a fan of fusible links.

Highly recommend an oil pressure safety switch. It is very minimal work to install, and could save your rig and your life.

 

[70_Steve]

If you "just need it running for the winter" (and I know how that goes!), there is wire #904, which is a Green w/Red stripe wire that goes from the ignition switch to the Voltage Regulator on the fenderwell. It is a Hot-In-Run wire. Tap into it under the dash at the ignition switch or in the harness that runs through the engine compartment. If you want it fused, then put a fuse in the line. Fuses and inline holders are cheap at any box auto parts store.

To do it "right", use 904 to energize a relay, and have the relay switch power to the fuel pump. For safety wire an oil pressure safety switch or inertia switch in line to the pump.

All things considered, it's not really that much more work to do it right the first time.

 

[Gould]

Gentlemen,
Wow. Thanks for the great replies.
I won't be able to tackle this until Saturday and I should be able to get some parts from my local parts guy to do that fuse (minimum) and maybe the relay and/or inertia switch.
Steve, I think your comment about doing it right carries a lot of weight. Thank you for that.
By the way, I will also be refurbing and reinstalling the auxiliary tank this weekend. My parts are due to arrive on Wednesday. (The tank fell off the truck when everything that was holding it in place rusted out.) Did I mention I will be doing a rebuild next year?
Gould

 

[BroncoBrandon]

Gould : Thank you for posting this question. I am wiring in my pump this weekend and I was about to ask the same thing..


(I may need to get out my fire suit for this question)
What is an inertia switch and shy should I install one?

 

[70_Steve]

What is an inertia switch and shy should I install one?

http://compare.ebay.com/like/330798563973?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

http://en.wikipedia.org/wiki/Inertial_switch

 

[BroncoBrandon]

Thanks Steve.

 

[707Bronk]

If you "just need it running for the winter" (and I know how that goes!), there is wire #904, which is a Green w/Red stripe wire that goes from the ignition switch to the Voltage Regulator on the fenderwell. It is a Hot-In-Run wire. Tap into it under the dash at the ignition switch or in the harness that runs through the engine compartment. If you want it fused, then put a fuse in the line. Fuses and inline holders are cheap at any box auto parts store.

To do it "right", use 904 to energize a relay, and have the relay switch power to the fuel pump. For safety wire an oil pressure safety switch or inertia switch in line to the pump.

All things considered, it's not really that much more work to do it right the first time.

Not meant to be controversail, but what is the advantage of using the #904 wire as opposed to hooking up to the Ign post of the Starter Solenoid? I hooked mine up to the solenoid because it also energizies the Ign Coil when the Ign is set to "run". Again, I'm trying to be informative, not controversial.

Is it an either/or, or is there a reason why the #904 is a better route?

 

[70_Steve]

Not meant to be controversail, but what is the advantage of using the #904 wire as opposed to hooking up to the Ign post of the Starter Solenoid? I hooked mine up to the solenoid because it also energizies the Ign Coil when the Ign is set to "run". Again, I'm trying to be informative, not controversial.

Is it an either/or, or is there a reason why the #904 is a better route?

No, it is not true that the solenoid powers the ignition coil when in RUN. In RUN the ignition coil gets power through the resistor wire, connected to the ignition switch. The only way the I terminal on the solenoid gets power in RUN is through the resistor wire which is also supplying current to the coil. The purpose of the I terminal on the solenoid is to bypass the current limiting resistor wire, and supply full power to the coil when starting.

In RUN, the only way that I terminal gets power is by being backfed from the junction with the resistor wire. By powering a relay from that terminal, you're reducing the available current to the coil.

 

[707Bronk]

No, it is not true that the solenoid powers the ignition coil when in RUN. In RUN the ignition coil gets power through the resistor wire, connected to the ignition switch. The only way the I terminal on the solenoid gets power in RUN is through the resistor wire which is also supplying current to the coil. The purpose of the I terminal on the solenoid is to bypass the current limiting resistor wire, and supply full power to the coil when starting.

In RUN, the only way that I terminal gets power is by being backfed from the junction with the resistor wire. By powering a relay from that terminal, you're reducing the available current to the coil.

Gotcha. That makes complete sense. I have mine wired with a relay and pressure switch, and it looks like I need to find a new power source to activate the relay. Even if the relay requires minimal amps to energize it (less than 1 amp) it is still taxing the coil.

I found a diagram similar to how I have it wired (I wired the presure switch a little different). Even though it looks like this is a standard way of wiring, I still do not like the idea of taxing the available coil amerage.

Edited----> I forgot that this was the way I had it wired before I rewired the whole rig. I went out and looked again and now I have a dedicated circuit from the fuse box to the oil pressure switch.