Inertia Switch

[Bucketlist]

I picked up an inertia switch from https://www.pegasusautoracing.com/productdetails.asp?RecID=87 and plan to install it since my air meter switch circuit is not wired and the fuel pump could continue to run in an accident. Has anyone installed one of these? Where did you mount yours?

[bigtim01]

I have not installed one on my Porsche, but I have installed one on the electric fuel pump in my 32 Ford, and I have one installed on MY Factory 5 Cobra. They can be tested by hitting the frame with a hammer. I also installed roll over shut off switches. I pick these items up at the u-pull it junk yard mostly from Ford products.
HTH
Tim

[flightlead404]

I'm not sure I'd run all the power for the fuel pumps through it. Check the switch rating. I think that's a 25A circuit. I'd use it to interrupt the ground side of a relay.

[Bucketlist]

Originally Posted by flightlead404

I'm not sure I'd run all the power for the fuel pumps through it. Check the switch rating. I think that's a 25A circuit. I'd use it to interrupt the ground side of a relay.

Your right. I went back and read it again:10 Amp continuous load rating allows the switch to handle the current of most electric fuel pumps (such as Facet low-pressure pumps) directly. Fuel pumps drawing 10 amps or more (such as the Bosch 044 and Aeromotive A1000 pumps) should use this switch to break contact on the fuel pump relay coil circuit.
So yes, this will be the plan.

[T77911S]

you could still wire it to the gnd side of the FP relays.
if you have the boost pressure switch you can wire it in series with that

[flightlead404]

Originally Posted by T77911S

you could still wire it to the gnd side of the FP relays.
if you have the boost pressure switch you can wire it in series with that

I agree with this. Switches s/b low amp circuits that control power to the suitably rated relay that controls the high current pump circuits(s). Inertia, air flow, and overboost switched can be inserted between relay coil and ground.

[Bucketlist]

Quote:
Originally Posted by T77911S
you could still wire it to the gnd side of the FP relays.
if you have the boost pressure switch you can wire it in series with that

Originally Posted by flightlead404

I agree with this. Switches s/b low amp circuits that control power to the suitably rated relay that controls the high current pump circuits(s). Inertia, air flow, and overboost switched can be inserted between relay coil and ground.

This looks like the best way to go. Since I have no overboost relay and only 1 fuel pump relay I just need to find the best place to splice into the fp relay ground (85) wire. I have also been looking for the best place to mount the switch. I really wanted this in the passenger compartment but the kick panels have thick carpet that I don't think I want to disturb. I was looking on the passenger side of the frunk where there is a clear vertical area. This is over the right front wheel area which might be a problem. Still looking, any advise?

[Ayles]

I put mine in the smugglers box. It was easy to cleanly route the wiring and there was a nice flat surface to work with.

[Bucketlist]

Originally Posted by Ayles

I put mine in the smugglers box. It was easy to cleanly route the wiring and there was a nice flat surface to work with.

Sounds like a good idea, wouldn't get tripped by accident, too bad my smuggler's box is full with the ac evaporator.

[Bucketlist]

Originally Posted by Ayles

I put mine in the smugglers box. It was easy to cleanly route the wiring and there was a nice flat surface to work with.

How did you wire yours in? I was going to pull the fuse box away from the fender and splice into the fp relay ground unless I find a better way.

[Ayles]

Mine is wired in at where the fuel pump relay is on an SC. I have carbs so it's wired like an older car, pump runs with key on. Hence the need for an inertia switch. I made a nice harness for it using shrink tube and expandable sheathing.

[Bucketlist]

I'm going to bring this old thread back up since I never did install that inertia switch a few years ago and might have time to give it another try.
This is an 81 SC body with a 930 turbo motor and one 044 pump. There is no yellow relay, over boost or rpm, and the pump runs with the key on.
Directions say to wire it into the hot side of the fuel pump #30 red wire?
Some of you guys posted back then that the ground side of the relay would be better. I'm a few years older but not any smarter. I think the relay ground sounds like the way to go but don't remember which wire that is. I have the fuse box loose and just need to pic the right wire. I thought it was #85 back in the day, someone straighten me out so I only have to do this once.

[boosted79]

Search "Another 930 teardown" and go to post 144

[spuggy]

Originally Posted by Bucketlist

This is an 81 SC body with a 930 turbo motor and one 044 pump. There is no yellow relay, over boost or rpm, and the pump runs with the key on.

Unrelated, but my '77 6-pin CDI did not limit RPM (because it expected the rotor to do that), and the '78 930 has a solid rotor (because CDI boxes from 1978 up do limit RPM - pretty sure I read this somewhere in PP).

So I think your SC CDI box should limit RPM. It's probably higher than the red line on a 930 tach (and a long way past peak power) though. Or there are several rotors that do limit RPM that will fit the 930 dizzy. They cut somewhere past 7K, IME, so don't do that with stock rod bolts....

You don't really need overboost if you don't monkey with the wastegate, or turbo timer if you don't kill the ignition on a red-hot turbo.

The pump running with the key on; my money is on there being a mismatch on the 930 (motor) wiring harness where it connects to the SC 14 pin plug. Seem to remember figuring it out once by comparing pin assignments on the car ('77 in my case) and 930 wiring diagrams. And then never bothered to correct it. If you do though, you could just make the switch on the AFM turn the relay for the pump on/off like the factory intended.

Additionally, on my '77 there was at least one completely redundant/unused wire from the original CIS running from the 14 pin plug to the front fuse panel (and disconnected there, IIRC) that could have been used instead.

[Bucketlist]

Originally Posted by boosted79

Search "Another 930 teardown" and go to post 144

Ford Taurus inertia switch between 30 and 87a of the air meter relay socket opens the ground side of the pump relay coils.

Mental block here - I don't think I have the air meter relay socket. It would be in the rear fuse box, correct?

[Bucketlist]

Originally Posted by spuggy

Unrelated, but my '77 6-pin CDI did not limit RPM (because it expected the rotor to do that), and the '78 930 has a solid rotor (because CDI boxes from 1978 up do limit RPM - pretty sure I read this somewhere in PP).

So I think your SC CDI box should limit RPM. It's probably higher than the red line on a 930 tach (and a long way past peak power) though. Or there are several rotors that do limit RPM that will fit the 930 dizzy. They cut somewhere past 7K, IME, so don't do that with stock rod bolts....

You don't really need overboost if you don't monkey with the wastegate, or turbo timer if you don't kill the ignition on a red-hot turbo.

The pump running with the key on; my money is on there being a mismatch on the 930 (motor) wiring harness where it connects to the SC 14 pin plug. Seem to remember figuring it out once by comparing pin assignments on the car ('77 in my case) and 930 wiring diagrams. And then never bothered to correct it. If you do though, you could just make the switch on the AFM turn the relay for the pump on/off like the factory intended.

Additionally, on my '77 there was at least one completely redundant/unused wire from the original CIS running from the 14 pin plug to the front fuse panel (and disconnected there, IIRC) that could have been used instead.

I have twin 8 pin CDI boxes with twinfire, maybe dates to '76

Never worried much about an overboost relay, only keeping my DOD adjusted so I don't hit 1.4 bar at 7k. It comes up soooo fast.

I think most of the '76 turbo pieces were swapped into this build, I don't think there is a 14 pin plug, at least I've never seen it.

Thanks for the Ideas, I seem to have a mental block on this.
I'll be a day older tomorrow and maybe this fog will clear.

[boosted79]

What does the SC use to shut the pump down in event of an accident? There has to be something. Wire the inertia switch in place of it. It should be on the ground side of the pump relay coil.

[Bucketlist]

Originally Posted by boosted79

What does the SC use to shut the pump down in event of an accident? There has to be something. Wire the inertia switch in place of it. It should be on the ground side of the pump relay coil.

That is exactly what I'm looking for.....which wire is the ground side of the pump relay coil? I'm sure this is the right place to wire in the inertia switch.

[boosted79]

On my 79 930 it's 87a that goes to grd thru the boost limit sw. If you know what the relay coil wires are just check which one shows 12v with the key on. The other one goes to grd

[spuggy]

Originally Posted by Bucketlist

I have twin 8 pin CDI boxes with twinfire, maybe dates to '76

Yeh, OK. Pre-78 don't rev limit, my understanding. Like I say, you can use a rev-limiting rotor in the dizzy instead for some protection. Unless you use an MSD or something that demands a solid rotor.

Originally Posted by Bucketlist

I
I don't think there is a 14 pin plug, at least I've never seen it.

It's on the front/left of the engine bay as you're standing looking at the motor, mounted on the end of the shaped metal plate that houses the CDI, the relays, small fuse panel etc. It's where the chassis harness terminates - and that plug connects the motor harness to the chassis harness and said relays etc.

Worth checking for corrosion and/or root vegetables on the contacts, although the plug/socket are similar to (if not actually) bakelite and can get kind of brittle.

Also where the infamous "yellow wire" to the solenoid (on pin #14) makes an appearance.