On the advice of several folks here I got an inertia shutoff switch for my fuel pump. The switch has three wire terminals that have tiny little markings. They appear to say: NC , C , NO. Which is what??
C = Common NC = Normally Closed NO = Normally Open The NC will have continuity with the common when the switch is in it's normal state.
Er..OK. I figured it would be something like 1. Power in, 2. Power out to pump, 3. Ground. How do I wire this?
Your only going to use 2 of the terminals push the switch in and find which 2 of the 3 have continuity smack the switch and make sure the continuity is no longer there 1 wire in 1 wire out it don't matter which is which Ford only used 2 wires and you should be able to get a connector from a ford dealer bring the switch with you
Hell, I hadn't heard of this before but the more I think of it an inertia switch on a hot rod is a damn good idea. Are a lot of guys using them?
First of all be advised Ford inertia switches only operate a relay. The relay takes the Fuel pump's load. I don't think the switch is rated to handle the actual pump current. As for wiring it. Bring power to the C ( common) and the output to the fuel pump relay goes from the NC ( normally closed). The NO (normally open) side is to activate a lamp on the dash to indicate that the inertia switch has been tripped. In the "tripped" condition ( NOT NORMAL!) the NC side goes open and cuts the fuel pump power and the normally open side closes and lights the warning lamp. HTH Stu
most that run electric pumps should, only a few that I know actually do, but its a good idea I rigged up 1 to the power feed to the coil so it will kill the motor on a hard impact I run a mechanical pump Made sense to me
A couple of people on here suggested it, and coincidentally an article in R & C mentioned it right about the same time, so I took it as a sign. This is the first I've heard that it is only to run a relay though.(Thanks for that info Stu). FWIW if you buy the switch at the dealer, do not buy the wiring kit they sell with it. It is almost as expensive as the switch itself (about $20) and has about a buck worth of stuff in it, all of which is probably already in your toolbox.
Depends on the application I'm sure. IIRC the early Ford EFI stuff used a relay. This is a later switch as the early ones had no warning light feature so it may be well rated. On a general note, make sure the switches rating is up to it's usage. No one wants a melt down that will leave you on the side of the road or worse on fire! Stu
I wouldn't run the load of the pump through the switch, it's just good practice electrically to have a relay. If the switch fails with only the switch, you're screwed. For safety sake, you want to wire it in such a way that it is in a fail-open configuration. Assuming that NC is in reference to a non-tripped postion, Run a switched 12V to the common, then the NC to the pin on the relay that, when energized, closes the fuel pump circuit. That way if power is lost to the switch, it will open the relay and kill the circuit. (It sounds obvious, but you can wire it the other way just as easily) Run a relay... Even if Ford didn't, its good practice. And it gives you the option to run anything else you may need off the same inertia switch as well, like the ignition or anything else that you can think of.
Actually it depends on how rough your ride is and how bad the roads are where you live. Ask me how I know that one. I'm not nixing the idea just consider this food for thought. I've run a roll over switch on 'em, and even run 'em past an oil pressure switch no oil pressure no fuel.
\well, i'd run the pump with the inertia switch just like ford did. ever see a relay stick? i have, lot of 'em.... factory fuel pumps take about 6-8 amps plus the overkill factor....
I checked the wiring diagram I have for a '90 Ford. They operate a relay with the inertia switch. The sticky relay is a valid point but in my experience with EFI Fords the relays usually stick in the OFF position!!!! Requiring a nice hard rap to get them to work!
Anytime something is going to be a saftey device and its main objectiive is to cancel an operation (shut something off) if should fail open and not closed. Its a redundency thing but that way a failure of the device won't cause a lack of saftey.
Not having the item in front of me, I will ask a (maybe) stupid question. How do you reset the system after a shutdown event?
As an EE, I wouldn't. It's bad practice, whether it's factory Ford or not (I would bet a MILLION dollars that the only reason it is done by Ford is to save the extra $0.75 that a relay would cost). Every relay I have ever seen stuck closed is from bad design/installation, not bad parts. Pull more current through a relay than the contacts are rated for and it'll weld 'em closed. People will think because their device pulls 9A that a 10A relay will due, but they forget to take into account things like the turn-on current draw of any motor, the losses caused by undersized/poorly terminated connectors/wire, etc. Not to mention all the "extra" things you can safely do if you use a relay, like a kill switch, tripped light, other switches, etc. Plus you have more options as far as switch placement, run the switch alone and you'd need to run heavier gauge wire all over the place. Run a relay, put it near the battery (which is also a safety thing), and you can run 18 AWG wire between the switch and relay safely. I always favor a setup where the control circuitry and the power circuitry are separated as much as possible, the closer they are to independent systems the safer I feel.
any of you guys wanna bet? 100 bucks sez i'm right and you're wrong!and if i ever figure out how to post a pic, i can prove it.
btw, most oif 'em where mounted under the heater box or kick panel on the trucks and the cars generally had 'em in the trunk area. why? don't ask me, i'm not an EE
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