Electric Fuel Pump Inertia Switch

[Sam Buchanan]

The Carter electric fuel pump I installed last year to replace the mechanical pump has worked flawlessly. However, every few months someone on the forum will mention how I will burn to a crisp if an accident disables me without disabling the pump. I've always considered this a very unlikely scenario (the ignition key turns off the pump) but the recent discussion about using an oil pressure switch with an electric pump prompted me to revisit this topic. I don't like the oil pressure switch solution because it interrupts the normal operation of the pump. But an inertia switch is totally transparent unless a hard jolt causes it to trip.

 

But how hard a jolt would it take? The internet is full of reports of false trips in Fords that use the switch, often triggered by potholes or out-of-balance tires. I don't like the idea of a single-point failure in the fuel pump circuit leaving me powerless in traffic......but there is a safety aspect. I decided to get a Ford inertia switch and see if it is a good option on the P15.

 

But......before I commit to trusting a FORD (!) part to keep me from getting rear-ended when the pump dies unexpectedly I decided to road test the switch for a few weeks to see if false trips are a problem. I soldered leads to the three terminals and mounted the switch to the firewall where it could be easily reached if it needed to be reset . The center terminal is POWER, one terminal is PUMP and the other is for a lamp to indicate a trip. I wired one side of a test lamp to the power lead, the other side of the lamp to the battery, and the TRIP lead to ground. This way the lamp will only illuminate if a trip occurs. I'll drive the car for awhile and check to see if the lamp comes on. If it doesn't trip during routine ops I'll feel more comfortable with wiring the switch into the pump circuit. A hard rap of the firewall with a screwdriver handle will trip the switch and turn on the lamp as seen in this photo, the switch is at the arrow:

 

 

 

 

 

Edited April 23, 2020 by Sam Buchanan

[DJK]

If you mount it inside the vehicle w/in reach and you have a lite to indicate it has tripped, you could reset it before carb runs out of fuel!!!!?????

[Sam Buchanan]

9 minutes ago, DJK said:

If you mount it inside the vehicle w/in reach and you have a lite to indicate it has tripped, you could reset it before carb runs out of fuel!!!!?????

 

Kinda...sorta. The switch needs to be attached to solid body structure and I don't know where you could do that and still reach it from the driver's seat. In Fords the switch is located behind a trim panel on the interior side of the body. Maybe on the firewall up under the dash somewhere?? I'm still pondering this.....if that thing trips when it isn't supposed to it won't be wired into the car.  ?

Edited April 23, 2020 by Sam Buchanan

[Sniper]

I've owned and/or driven a multitude of Ford's with that switch factory installed,

 

Zero trips and that even included me 4 wheeling, bouncing down caliche lease roads at ludicrous speeds because, hey it's a company truck.

 

I think the problems you mentioned are more overblown than real.  BTW, do you have the part number?  Been thinking of putting on my Cambridge since I am going EFI.  If I go the oil pressure switch route I will likely use the start 12V to run the pump in start, thru a relay of course, temporarily bypassing hte oil pressure switch.

 

 

[DJK]

37 minutes ago, Sam Buchanan said:

 

Kinda...sorta. The switch needs to be attached to solid body structure and I don't know where you could do that and still reach it from the driver's seat. In Fords the switch is located behind a trim panel on the interior side of the body. Maybe on the firewall up under the dash somewhere?? I'm still pondering this.....if that thing trips when it isn't supposed to it won't be wired into the car.  ?

Nissan used them in the early Quest(Mercury Villager), mounted on the left kick panel.

[Sam Buchanan]

25 minutes ago, DJK said:

Nissan used them in the early Quest(Mercury Villager), mounted on the left kick panel.

 

Some of the Fords have them on kick panels as well. That isn't a good option for me because I have a carpet panel that is screwed to the body work.

[Sam Buchanan]

52 minutes ago, Sniper said:

I've owned and/or driven a multitude of Ford's with that switch factory installed,

 

Zero trips and that even included me 4 wheeling, bouncing down caliche lease roads at ludicrous speeds because, hey it's a company truck.

 

I think the problems you mentioned are more overblown than real.  BTW, do you have the part number?  Been thinking of putting on my Cambridge since I am going EFI.  If I go the oil pressure switch route I will likely use the start 12V to run the pump in start, thru a relay of course, temporarily bypassing hte oil pressure switch.

 

 

 

There is a link to the switch in my first post but if you search eBay for 'Ford Inertia Switch' you'll find them. There sure are a lot of YouTube vids and forum threads about how to troubleshoot the switch...seems they can be a service item. But there are a lot of Fords out there that run with no issues.....I've never had one trip on the Fords I've owned.

Edited April 23, 2020 by Sam Buchanan

[DJ194950]

Has anyone checked into whether these switches need to mounted a particular way. Horizontal, vertical, does not matter?

 

Seems to me that the one I looked at in a Continental I had (a very short had) was in the trunk side cover  under a easily removed panel and was mounted horizontally.

 

Like this idea better myself than a oil pressure switch but each to their own.

 

DJ

[YukonJack]

I recall having seen them trunk mounted as well. I would think being trunk mounted is a better idea anyway. Usually if someone is going to hit you it's most likely going to be from behind. I would think if it were in the passenger compartment you'd have to get rammed harder to activate it. 

[YukonJack]

I think 90's Ford Escorts and Tempos had them in the trunk area too. On the drivers side.

[Sam Buchanan]

27 minutes ago, DJ194950 said:

Has anyone checked into whether these switches need to mounted a particular way. Horizontal, vertical, does not matter?

 

Seems to me that the one I looked at in a Continental I had (a very short had) was in the trunk side cover  under a easily removed panel and was mounted horizontally.

 

Like this idea better myself than a oil pressure switch but each to their own.

 

DJ

 

I played with the switch for awhile on the bench. Every time I've seen one mounted in a YouTube video it is oriented with the red button 'UP'. I found the switch seems to be sensitive to shock delivered laterally but has little sensitivity to vertical shock. Guess this is why I've seen it mounted button up and that is how it is mounted on my firewall.

 

As far as the location of the switch is concerned....if it is mounted solidly to the body it should receive quite a jolt if the car is hit hard on any quarter. The purpose of the switch is to interrupt power to the fuel pump only after a really hard collision. Any more sensitivity could lead to nuisance trips. If the collision is minor I just reach over and turn off the ignition.

 

Trunk mounting is certainly a possibility for my car since the fuel pump is located near the tank, that would make wiring pretty simple.

 

But hey....I've only had this thing for a few hours so what do I know.......   ?

Edited April 23, 2020 by Sam Buchanan

[Tooljunkie]

Only failure issues i have ever seen is the terminals melt. Usually a pump going bad and causing excessive load. 
other failure is moisture,and corrosion. Seen green wires under the carpet. 
 

never really thought about using an inertia switch, not a bad idea. 
2 rangers in the back yard, could source one there if i wanted. 

[maok]

You could use both, an oil pressure switch as well as an inertia switch in parallel so that BOTH would need to trip before the fuel pump is disabled.

[Sam Buchanan]

1 hour ago, maok said:

You could use both, an oil pressure switch as well as an inertia switch in parallel so that BOTH would need to trip before the fuel pump is disabled.

 

That is getting way too complicated for my 1948 car......I could just forget about the inertia switch and drive happily ever after......   ?

Edited April 24, 2020 by Sam Buchanan

[maok]

4 minutes ago, Sam Buchanan said:

 

That is getting way too complicated for my 1948 car......I could just forget about the inertia switch and drive happily ever after......   ?

 

Series wiring is easier...?

[MackTheFinger]

My kid had a '92 Ford Escort about 20 years ago. I bought it from the son of the original owner and gave it to the kid. He called me late one Saturday night to tell me his car had broken down. He had gotten lost and ended up on Skinker north of Delmar in St. Louis. For anyone not familiar with the St. Louis area it's not really someplace you want to be late on Sat. night. He said the road had been resurfaced and he hit a drain or a manhole that hadn't been completely finished and the car stopped running. He'd managed to get it onto a side street and someone he knew in the city, someone who was armed ?; was coming to help. I told him to take anything of value out of the car, leave the doors unlocked, and I'd come up and pick it up in the morning. When I got there I exchanged pleasantries with the local crackheads and started checking it out. Sure enough, fuel pump wasn't running. I hauled the car back here and had dropped the tank when the guy I bought it from called and asked what I was up to. When I told him what I was doing he told me about the inertia switch. Said it had been flaky forever. Ford had replaced it under warranty a couple of times. I'd never heard of an inertia switch before then. The kid said it tripped a couple of times after that even without hitting a bump.

 

So, yeah; sometimes they do trip on their own.

[DonaldSmith]

Maybe you heard this before. 

20 or so years ago, my wife went to work, and my daughter and baby granddaughter left for home after a visit.  I was going to go to work, but became unusually tired.  I decided to sit in the recliner for a while. 

My daughter called (from a borrowed cell phone - this was twenty years ago).  Someone on the expressway had bumped her car, no damage, but the car would not run. 

I got to the scene, saw that the car would not keep running, and I immediately knew what to do.  I reset the inertial switch in the trunk, and they continued on their way.  

I think it was divine intervention that I had suddenly been so tired before setting off for work. 

[MackTheFinger]

2 hours ago, DonaldSmith said:

I immediately knew what to do.  I reset the inertial switch in the trunk, 

 

At least you didn't have to haul it 150 miles.... DOH!!!

[Sam Buchanan]

This is really encouraging.....  ?. ?

[kencombs]

25 minutes ago, Sam Buchanan said:

This is really encouraging.....  ?. ?

Sam, I think I'm the one that brought up the inertial switch and plan to use one on my pickup.  My play is to install an on/off switch in parallel with the inertial switch.  So, if it trips from a pothole,  ditch in the field or whatever, just flip the bypass which is normally off/open.  No muss, no fuss.

[dodgeguy]

Wow I live in St.  Louis, hope I never brake down on this Skinker street  mentioned or any place south of Cape Girardeau or further south say like Sikeston  LOL  all in jest of course I'm locked down here in St. Louis. But I feel like a teenager again  Gas is Cheap and I'm grounded.!!!! Wont be able to get through the front door! Even having groceries delivered not sure how that is going to work out yet.

[MackTheFinger]

The real tough part of St. Louis is around Adie and Ridgecrest. I saw a coupla thugs hanging around there that I wouldn't want to be on the bad side of.  Sikeston can be pretty rough for a little country town.. Somebody's liable to bonk you on the head with a biscuit. ?

[dodgeguy]

touche

[DJK]

Just a thought, the inertia switch could be used as a anti theft device, just activate it to disable the fuel pump!!!!!

[Sam Buchanan]

I think the best anti-theft device on the P15 is the column shifter!   ?

Edited May 2, 2020 by Sam Buchanan