Inertia switch necessary?

[Curious Hound]

During the electrical demo and combining of harnesses for my engine swap, I accidentally cut the inertia switch wires out of my harness. To put them back will require splicing in several places. So, my questions are;

1. How necessary is it?
2. Is it legally required?
3. What about location?

I'm considering 3 basic options.

First, just delete it and simplify the wiring. I know the safety reasons for it being there. But, how big a deal is it? There is always a chance while off-roading of bumping something that would "nuisance" trip it. Cars survived many years before its introduction.

Second, relocate it, most likely on the firewall in the engine bay, near the brake booster. That shortens the wiring and I probably would not have to splice anything. Still easy to access. I believe they put it in the cab because that should protect it more in the event of an accident and allow access so you can reset it and move the vehicle off the road. But, lets face it. If the accident is bad enough that it requires the cab to protect the inertia switch, resetting it isn't going to help the vehicle move. With this option, I still have it in the circuit to de-energize the fuel pump during an accident.

Third, splice all the wiring back together as the original harness was designed.

There might be a 4th option. The Explorer harness routed that wiring differently. I might be able to bastardize some hybrid routing. Not sure.

What do you think? What thoughts am I missing?

 

[alwaysFlOoReD]

In my pinto I put one on the inner fender.

 

[alwaysFlOoReD]

In my racetruck I used a pressure sensor on the oil pressure. That works if sideways or upside down. I did lots of jumps and rough runs in short course off-road.

 

[JoshT]

IMO...

Required, no. (Pretty sure it isn't legally required on anything this age anyway.)

Good idea, yes.

If you are going to be doing the type of driving where it is likely to trip often. Lots of offroad or very rough road driving. Very little if any on road driving. Delete it.

If you're going to be road driving a lot, keep it. It's there to kill the fuel pump in event of an accident so it isn't continually squirting a highly flammable liquid onto an ignition source.

Since you've got to rewire to reinstall it anyway, I'd relocate it to an easier to access location and do your wiring so that you can easily bypass it for offroad driving.

Alternatively put it back in original location, run your own wires, and create the bypass somewhere easy to access. For a bypass I'd use a 2 pin connector. Female connector on the harness side so that energized wires are protected if it comes loose. Male connector on switch side. Second male connector looped so that you can quickly sweap them out. You could also just use insulated spade or bullet terminals, but I like the neatness of a connector.

 

[Roert42]

Put it whatever it’s easiest to install and leave it.

If it ever trips, install a toggle switch to bypass it in the cab, but leave it enabled.
Then if you need to bypass it, you don’t have to get out and pop the hood ( for a second time), just flip the switch.

I’ll bet you’ll never get to step two.

 

[lil_Blue_Ford]

Over the years I’ve had to bypass three of them for a faulty inertia switch.

I’ve also been in three wrecks that totaled the Ranger. All three the inertia switch never tripped, I turned the key off. Those were not the same vehicles that I bypassed the switch either.

That doesn’t inspire confidence in the switch.

 

[rubydist]

I think it is very important - it will greatly reduce the risk of a fire in the event of a crash. It would be worth it to me to put back in.

 

[lil_Blue_Ford]

I think it is very important - it will greatly reduce the risk of a fire in the event of a crash. It would be worth it to me to put back in.

I used to think that, but after seeing 6 fail to do their job, I’m significantly less confident in the system

 

[scotts90ranger]

If you really think it through the computer has a timer on the fuel pump, if the engine stalls the fuel pump turns off so the only REAL reason to have an inertia switch is in the rare case you are in a hard enough wreck to trip it that also cracks a fuel line just enough to allow the engine to still run...

When I was in my fender bender a few years ago turns out the inertia switch was unplugged from the wife's foot not tripped (don't remember, but was definitely unplugged). I was also out hunting one day with me and a buddy in my '00 Explorer and it just wouldn't start, we were both overthinking it (he's a mechanic) but then it clicked and we both came up with the inertia switch at about the same time and sure enough it was tripped randomly...

I say delete it...

 

[pjtoledo]

location probably isn't critical. in the Taurus' 89-95 they were mounted behind the driver side rear tire.
we used to get out of the car and smack the rear fender to trip it. t'was a poor mans anti theft device.

 

[PetroleumJunkie412]

I yeeted mine.

I am a bad example.

 

[PlumCrazy]

I have only ever triggered one in my life and it was a false alarm. I have wheeled HARD and never set one off. (Even when I think it should have). So I could take it or leave it and have no regrets either way.

 

[SenorNoob]

Mine did trip when I wrecked. Probably a good thing or idling in that leaf filled ditch while I was unconscious would've probably started a fire under the truck. That meant I did have to bypass it to drive out though. It was 2 days later in the house when it could finally be reset. I put it back in.

I'd think anywhere on the firewall would be fine. Mine is held on with 2 factory self tapping screws. Pick a place and zip it in.

I like the oil pressure switch idea. Although that's a Chevy thing, with it's own problems.

 

[85_Ranger4x4]

In my racetruck I used a pressure sensor on the oil pressure. That works if sideways or upside down. I did lots of jumps and rough runs in short course off-road.

Right now my truck has to see tach signal before it will do more than prime the fuel system so it is kind of the same theory. If the engine isn't running no fuel.

I still have an inerita kill switch. It was there from before I had a computer commanding my fuel pump and I didn't really have a reason to remove it.

Worst case of it tripping is you bypass it. Worst case of it not tripping it pumps fuel into a fire.

 

[Curious Hound]

Worst case of it not tripping it pumps fuel into a fire.

It'll stop pumping eventually.