Inertia vs Oil Pressure Switch

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straightlinespeed

straightlinespeed

Sometimes I pretend to be normal
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Ive searched and it seems to be a back and forth debate. Im researching parts that I will be needing for when I rewire my car.

I've been debating about using the oil pressure switch or the inertia switch or both when I install a electric fuel pump.

Does anyone have first hand knowledge with either or both of these installed on there car?

I do have a couple questions myself. When using a 3 prong oil pressure switch (like in the pic below). I assume you actually have to have 2 switches installed. This one and the sender one? Like what it says in the pic, because this is not a sender???

View attachment switch.jpg

As for the inertia switch, how hard of launches can they take? Not like my car is a big power maker, Im just trying to find out how much it takes to trip them? That could be a embarrassing if you launch and they trip.

I would like to hear from those of you that have these items installed how you like them.
 
I have used the OP switch for the last 25-odd years on various vehicles. Have one on my '65 Valiant, installed as described below. A pic or two in my sig linked build.

An OE application, if they're still available (Couldn't find it on Rock Auto) is one for a Chebby Vega. They had electric pumps and GM used such a switch to protect against fires.

You are correct, you still need a sender or switch for what ever is in the dash. What I do is mount a 1/4" NPT "T" to some place convenient (fenderwell, firewall, etc.) and put both sensor/switches there. Then I run an 1/8" copper tube from the sender/switch port on the engine to the last port in the "T". Be sure to leave a loop or some considerable extra length for vibration induced fatigue relief.

One vehicle I wired using this switch had only that switch to turn on and off the fuel pump. Worked great, about the time that the driver closed and locked the door after a long drive the pump would quit.
 
My old ranger had an inertia switch and the only time it ever got tripped was when I t-boned a corolla after it made a right turn from the left turn lane.
I suppose it would depend on what kind of inertia switch it is and what g-force it's rated to trip and where it's installed.
 
I bought one and it didn't seem to trip waving it around in my hand unless I actually slapped it against my other hand. I too was concerned about hard launches but I'm going to try it out and see how it goes.
 
Inertia switch....to me it is a good idea. Have seen some folks say that they are to touchy....just go to you tube and search for ADD Ford Raptor...and watch some of the videos...Takes a lot more than a pot hole or the force of a launch to make it break the connection...
 
Thanks everyone. I know my fiances inertia switch in her Ranger didnt trip when she spun out one winter and hit the ditch, and rolled it onto the side. The truck stayed running. So it must take a heck of a shock to trip it. I think I will pick up one of each switch and wire them in. I would rather be safe.

I'll also look for that Vega OP switch
 
Both are nice, but IMO the inertia switch is sorta stupid for a carbureted car. It is going to keep running regardless of whether it sees fuel pressure. At least until the float bowls are empty. That could be a good while idling after a wreck. Of course, it would stop the flow of fuel, which is good, but if you want the engine to stop, you need some type of ignition kill. No doubt in my mind that you could wire in the inertia switch to kill the fuel pump and ignition both at the same time.
 
RustyRatRod said:
Both are nice, but IMO the inertia switch is sorta stupid for a carbureted car. It is going to keep running regardless of whether it sees fuel pressure. At least until the float bowls are empty. That could be a good while idling after a wreck. Of course, it would stop the flow of fuel, which is good, but if you want the engine to stop, you need some type of ignition kill. No doubt in my mind that you could wire in the inertia switch to kill the fuel pump and ignition both at the same time.
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That is a good point you make!
 
Why does the 3rd wire go to the starter, and which one? The large one from the battery,or the smaller one? Can't it go to the starter relay?
 
Tough call. My only experience is the hundreds of inertia switches I have replaced on Fords. I assume anyone and everyone can make a part better than Ford, but it still makes me worry.
 
Mopar to ya said:
Tough call. My only experience is the hundreds of inertia switches I have replaced on Fords. I assume anyone and everyone can make a part better than Ford, but it still makes me worry.
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Why did you have to replaced them? I was thinking of hitting up U-Pull and grabbing one.
 
They just fail. Car gets towed in for crank no start. You get down to fuel pressure - it's zero. Oh, needs a fuel pump! Not. Check power and ground and you don't have them. I'm sure there are aftermarket inertia switches that are better quality, but don't buy a Ford unit.
 
Mopar to ya said:
They just fail. Car gets towed in for crank no start. You get down to fuel pressure - it's zero. Oh, needs a fuel pump! Not. Check power and ground and you don't have them. I'm sure there are aftermarket inertia switches that are better quality, but don't buy a Ford unit.
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Ahhh I gotcha, Thanks
 
straightlinespeed said:
I believe it goes to the large battery wire and that is so you can bypass the switch when there is no oil pressure. Im sure it can hook to the relay also. Here is the link I got that pic from.. You look at it and let me know your thoughts

http://www.how-to-build-hotrods.com/electric-fuel-pump.html
Click to expand...
It goes to the "Start" wire terminal either at the starter or at the starter relay on the firewall. Basically it by-passes the switch while cranking. Can get fancy and do this other ways, but this is a simple way to do it, and w/o a relay for the pump. I've run Holley Blue's directly off that switch with no relay in the circuit. Worked fine for several (5+?) years until the truck was rolled by being t-boned on the Grapevine.
 
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