Oil pressure safety switch

[6packCuda]

Today I installed an oil pressure safety switch for my elec. fuel pump. Before installing the switch, the pump worked fine. Now it doesn't work. I know I've probably got a wire wrong somewhere, but I don't know which. Here's what I've got....the red lead from the pump is fused and goes to the "C" terminal on the switch. I have a wire going from the neg. side of the coil to the "NO" terminal on the switch. I have a wire going from the smaller gray wire on the starter solenoid to the "N" terminal on the switch. Should the "N" wire be hooked directly to the starter solenoid or to the solenoid box on the fender? Right now it's hooked to the fender box.

[GoodysGotaCuda]

Sorry i'd help but you've got me lost. So you are tryingto tie both your fuel pump and coil into this safety swtich?

Whatever it is your pump doesn't sound like it has any power besides in the 'start' key position given you hooked it to that wire on the starter solenoid? Been a long day and i may have something mixed up, any install diagram that came with it?

[GoodysGotaCuda]

Found this

http://static.summitracing.com/global/images/instructions/sum-g1438.pdf

Sounds to me like you have a couple issues.

1) this particular one is rated at MAX 5amp draw, which the average fuel pump is going to draw more than that. You'll eat that switch up fairly quick.

2) You should really have your fuel pump wired on a relay. Easier on swiches, easier to wire up (as in you wont have to worry about burning that oil psi switch you just got), and you'll get more consistant voltages.

3)Nowhere does it state the wire on the starter solenoid. That wire is only hot during cranking. Therefore your fuel pump may work while you crank, but will not run when you let go of that key position. And it will not work until you get sufficient oil pressure to close the contacts.

Where was the fuel pump wired up before for power? Thats where the other side of the switch needs to go, instead of the starter solenoid.

[6packCuda]

Sorry, I guess I wasn't very clear. I'm not very good at explaining these things because I really have no idea what I'm talking about. Ok, I'll try again. The diagram that came with the switch shows the hot wire from the pump going to the "C" terminal on the switch. There's a wire going from the "NO" terminal on the switch to the ignition switch. (This is the wire that I ran to the neg. side of the coil.) Maybe that was wrong. Then the diagram shows a wire from the "N" terminal of the switch to the starter solenoid. (this is the wire I hooked to the fender box where the starter solenoid wire is.) I'll attempt to copy the diagram to this.

http://static.summitracing.com/global/images/instructions/hly-199r10367.pdf

[73EStroker]

OK we try to help/explain here.

Take a fused 12V source from somewhere like the main battery terminal connection. Same place as where the 10AWG fusible link (should) come from. Take this wire through an inline fuse (10A should be enough) then go to common (C) on your pressure switch. From normally open (NO) on the other side of the pressure switch go to the fuel pump (+) then ground the fuel pump (-) to a good ground. This means the pump will only run when you have oil pressure. I take it this is a stand alone oil pressure switch to do just this job - IE not connected to anything else in the car.

By doing this you are not adding extra load to an already taxed (by age) 35+ year old wiring/component system. Use the correct size crimp lugs where you are connecting to the bolt at the battery and where there are screw type terminals. Don't short cut, improper wiring will bite you when you least expect it.

Now the better way to do this is by relay (as stated earlier in this thread) to take the load away from the oil pressure switch. That is a little more complicated circuit and if you want put your email here and I can draw you a circuit and PDF/scan the diagram and send it off to you.

[6packCuda]

Thanks 73EStroker. I'll try it like you said, but don't I have it hooked up just like the diagram from summit shows. It seems to me, with it wired the way I have it, there should be power to the pump when the key is in the on position and when cranking. I don't know. Maybe I'll take it all back out and re-do it with a relay. I've seen two different diagrams from Holley for this pump. One says to use a relay, the other does not. One says to use a 7.5 amp fuse on the hot wire to the pump, the other says a 10 amp fuse. What's a guy to do. Oh, and if you could send me that diagram I'd really appreciate it.

Dave
d_wamboldt@hotmail.com

[GoodysGotaCuda]

Many of us would have our own ways of wiring up the switch. Here is how i would do it, with the 'optional' toggle so you wont have extended cranking. Yes the switch is now working a ground rather than the power side, will work just the same, just another way to do it. This would be the simplest form i could think of 


edit: actually an easier way to work the toggle in that way, is you dont need to run a wire from before the switch, to toggle, to after. just run to the pump side of the switch, to the toggle, to a dash ground.

[GoodysGotaCuda]

oh and i run a 10a fuse on my holley blue pump

[Chryco Psycho]

run power through the relay from a good power source with a fuse or fusable link , then ground the relay at the oil pressure switch as soon as there is pressure the pump will turn on , if you lose pressure the fuel pump is off

[6packCuda]

I think I might have figured out the problem with the setup I have. I havn't tried it yet. But, I have a MSD 6A ignition, so I'm thinking the wire I have connected to the neg. side of the coil should be connected to the red wire coming out of the MSD box. Does that make sense to anybody?

[6packCuda]

Ok. I tried that and it seems to have done the trick. One strange thing though. I can just barely here the pump running now. It is a gerotor design pump that is suppposed to be quiet, but it was much noisier that this before. The only reason I know the pump is even running now is because, well the engine runs, but also when I shut off the engine I here the pump for just a split secod before it cuts off. When the engine is running, I can't hear the pump at all. So, while I'm happy that the pump is quiet, I'm also concerned as to why it's quiet now when it wasn't before. Do I have something wrong now, or did I have something wrong before?

[Chryco Psycho]

Hard to tell , was it pumping fuel before or just running dry ?

[6packCuda]

It was pumping before. I drove it all last summer that way. I had it wired differently. I just had it hooked to a wire I found under the dash that was hot with the key on and not with the key off. Now it's wired through the safety switch as I desribed in my other posts.