Installing electric fuel pump - do I need a relay?

[MEK-Dangerfield]

If his fuel pump is like the Mallory I had, he won't need rubber bushings/washers. Mine was so quiet you couldn't hear it running, so no vibration.

I do agree with getting rid of the glass filter on the input side. If you have a filter(sock) on your sending unit pick-up tube, that will be good enough. Just have a finer filter somewhere before the carb.


  Mike

[BruteForce]

Looks like I'll be taking the filter out. Thanks for the advice!

[6packCuda]

This may be a stupid question, but what does a relay do, and how do you wire it in for a fuel pump application?

[BruteForce]

It's not a stupid question, it's a very good one. A relay is is an electromagnet that, when energized with a small current, will cause a switch to close through which a large current can flow. So, you can control a large current with a small one, like power steering or power brakes.

Large current devices require heavy wires, fuses, and usually short wires. It would be unpleasant to stuff all that under the dash, and dangerous (large currents can, if not done right, start fires). Some fuel pumps can eat up to 30 amps, that just won't do to try and draw that through your ignition switch. So here's how to wire one up:

[BruteForce]

Here's the pic I just sketched out.

[6packCuda]

I have the Holley HP125 pump. When I installed it, I just ran the hot wire from the pump, to a wire I found under the dash that was hot when the key was on, and not hot when the key was off. No fuses, no relays. After reading this thread, I'm starting to think maybe I better do things differently. I drove the car that way all of last summer with no problems. Should I re-do it with a relay?

[BruteForce]

At a minimum, it needs a fuse. Without a fuse, if there's a short, you'll fry your wires and possibly even set your dash on fire. Put the fuse as far 'upstream' in the circuit as you can.

The instructions for the HP-125 pump say 12 gauge wire, 15 amp fuse, and a relay.

The oil pressure switch is there to shut the fuel off in case you get in an accident. The pushbutton is to 'prime' the carburetor so you don't need to do a lot of cranking if it's dry.

Relays are cheap and easy to install, my pump only draws 3 amps so it isn't really needed, but I'm kinda putting it in for fun.

[asm74]

BruteForce,
just curious, are you using a return line in your fuel system? 
I have pretty much the same system as you, except without the pushbutton bypass, looks like you've got everything done right!

[BruteForce]

Actually, I'm doing everything all wrong. In reading the instructions for the HP-125 pump, it says don't use teflon tape, it'll come apart and damage the pump. Naturally, I had put it together with teflon tape. So off it came, and I just got through cleaning the tape off. Will reassemble later tonight.

No return line, I don't think it's necessary for this pump, which is a low pressure/low volume one. I had bought a Holley super-dee-duper one, but the instructions said get a regulator, filter, return line, etc., which all seemed too much bother. If this setup doesn't work, I'll go back to the Holley and install all those extra expensive parts.

One reason why I'm putting in the relay now is I'll need it anyway for the Holley.

My main concern is keeping the lines away from the exhaust and everything out of the way of the axle. My eyeball measurements give me an inch or two clearance from the axle at max travel.

[BruteForce]

The first picture is my new, revised install (thanks for the suggestions!). The second shows the fuel pump relay socket mounted to the wall on the driver's side (the big red wire coming out of it goes to the battery, passing through the firewall through that unused rubber grommet Dodge helpfully put in for manual window washer tubes). I made a little bracket out of 16 gauge steel to mount to the left of the steering wheel to hold the switches. One is a momentary-on switch for priming, and the other is a manual kill switch for the pump power. They aren't wired up yet. I've left room for possibly adding more switches and an oil pressure idiot light, since the oil pressure cutoff switch will also power that.

I'll paint it black when everything is done.

[BruteForce]

Here's the other pic.

[hemiken]

Hey Brute,

I am soooo glad you took all of uor advice and got rid of that filter buddy.

Last thing you want is a driver that turns into a fireball, it would look impressive, but man would you be p!ssed. 

[422STROKER]

Looks like a clean install on the switch plate.  Nice job!


Tom

[BruteForce]

Thanks for the kind words! But I stink at metal work. No matter how carefully I measured the holes, center punched them, and drilled them, the holes wound up off 1/8". What saved me was I didn't have a drill bit big enough for the switches, so I filed them out to the right size and 'over a bit'.

Anyhow, I feel pretty good about how that turned out. I'm thinking of trying to build myself a new battery tray next. My old one is badly corroded. (I know I can just order a new tray, but where's the fun in that?)

I found a used anvil. Tomorrow I'm going to go pick it up.

[asm74]

I notice you removed the glass filter between the tank and the pump, but you did not replace it, why? 
I have a summit billet -an filter between my sending unit and my electric pump, as per the pump manufacturers instructions... is that a bad idea?