[ZeGermanHam]

I have installed an electric fuel pump in my GTO, and I am now in the process of wiring a fuel pump safety switch that shuts the pump off if there is no oil pressure. I think I understand most of what needs to be done, but since I'm a total novice with electrical stuff, I wanted to ask for guidance on one thing.

Here is the diagram that is provided with my pressure switch kit:



My question surrounds how to connect the "S" (starter) terminal of the oil pressure switch to the purple starter wire. Instead of the purple wire coming from the bulkhead and going directly to the starter, do I instead divert it to the oil pressure switch and then "T" it off and then go to the starter? I photoshopped the diagram below to show what I think needs to happen (see yellow circle). Am I thinking about this correctly?



Apologies for asking such a basic question. Electrical is not my thing. I think these two diagrams effectively show the same thing, but my brain seems to agree with the 2nd diagram more.

[Geoff]

That is correct. Oil Pressure sw. P=common; S=NC; I=NO

[Bill Hanlon]

I'd recommend leaving the purple wire that runs from the ignition switch to the starter solenoid un-molested and connecting a wire from the S pin on the solenoid to the S pin on the safety switch. That way you don't have to worry about splicing the wires.

As drawn, your circuit has no facility to make the pump run to pre-fill a carb that has been sitting for a long time. That would involve a push button that connected pins I and P on the safety switch.

[ZeGermanHam]

Thanks Bill. That is helpful, and I'd much rather not splice wires if I don't need to.

As far as pre-filling the carb goes, my understanding is that it shouldn't be a problem. You can't pre-fill a carb with a mechanical fuel pump either, so in that regard it's no different. As soon as you start cranking and a few PSI of oil pressure is generated, the pump will turn on, which should be pretty much instantaneous when turning the key to start.

[Bill Hanlon]

... some people also put a roll-over safety switch in place to cut power to the pump when the car isn't on all 4 tires. More of an issue with fuel-injected cars because carbs usually quit working when upside down and therefore the engine stops and oil pressure goes to zero.

[ZeGermanHam]

I may look into setting up a rollover safety switch in the future. I have built the car to be suitable for EFI (in-tank electric pump + return line), but I am going to regulate the fuel pressure down and run a carb for a little while after completing restoration. There is a good chance that I will swap over to EFI at some point in the future, and at that time a rollover switch would certainly be given some consideration.

Thanks again for your knowledge here. I've got plenty of mechanical skills, but this is my first rodeo with electrical. As a result, I am trying not to make assumptions that may be incorrect.

[misterp266]

You do realize that will not stop the engine from running right? You’d be surprised how long it will run without fuel pressure.
On my “race only” Tempest, I installed an oversized oil pressure light as well as a gauge. If the pressure dropped, I knew right away and could shut the ignition off.

[ZeGermanHam]

Yes I know it will not stop the engine from running, not right away anyhow. I would not want an engine to automatically turn off based on oil pressure alone. This safety switch design is used to prevent fuel from being pumped to an engine that has stopped running due to a wreck or mechanical issue.

[VCho455]

I've used one of these for years. A bit more money but, it powers the pump for three seconds on initial triggering to fill the float bowl.

https://www.revolutionelectronics.co...Fuel_Pump.html