Shrouded Push Button next to ECU - what is this for?
Discussion
I used to have a bad connection at the heater controls so used to tap the dash to get it working until one fine day when I tapped said dash to hard ( I thumped it) and activated the intertia switch at a T junction and promptly lost all power, after the AA had found intertia switch ( and showed me where the flaming thing was everything was a go again, soon got that connection sorted and didn’t attempt that again in a hurry,,, so they do work rather well!
ianwayne said:
Apologies for not realising it was the fuel pump inertia switch straight away! The OP said it was next to the ECU, mine is nowhere near it. The ECU is in the footwell and the reset inertia switch is up under the pouch flap.
Same with mine,,, which as a new owner I had no idea how to access it, AA man did a bit of homework and I felt a bit of a tit 
It was after this embarrassment I think I started to take a keener interest in all things Chimeara and slowly removed the myths
Classic Chim said:
I used to have a bad connection at the heater controls so used to tap the dash to get it working until one fine day when I tapped said dash to hard ( I thumped it) and activated the intertia switch at a T junction and promptly lost all power, after the AA had found intertia switch ( and showed me where the flaming thing was everything was a go again, soon got that connection sorted and didn’t attempt that again in a hurry,,, so they do work rather well!
Do they ever trip out on bumpy roads?Not in my experience, in all fairness I was whacking the dash 
served me right !
Considering how hard they feel on bumpy roads if you have stiff springs and low profile tyres it’s a suprise they don’t activate more often, I’ve buckled a wheel and blown a tyre hitting a new pot hole one time and that was a heck of a thwack but the intertia switch was fine. I was stationary so that might have had something to do with it.
Now you’ve got me thinking how do they work, I’ve got Brembo brakes and did loads of tests until I was stopping on a sixpence from high speed which had the back wheels almost off the ground and a lot of G force.
Another quality item of on our Tvr we don’t praise enough
served me right ! Considering how hard they feel on bumpy roads if you have stiff springs and low profile tyres it’s a suprise they don’t activate more often, I’ve buckled a wheel and blown a tyre hitting a new pot hole one time and that was a heck of a thwack but the intertia switch was fine. I was stationary so that might have had something to do with it.
Now you’ve got me thinking how do they work, I’ve got Brembo brakes and did loads of tests until I was stopping on a sixpence from high speed which had the back wheels almost off the ground and a lot of G force.
Another quality item of on our Tvr we don’t praise enough
Edited by Classic Chim on Friday 28th December 12:46
Classic Chim said:
.........Now you’ve got me thinking how do they work,..................
Only ever taken one inertia switch apart and that one worked with a ball bearing held onto contacts with a magnet.Shock caused the ball to break free of the magnets. Pressing the button pushed the ball back onto its seat.
Steve
Penelope Stopit said:
Classic Chim said:
I used to have a bad connection at the heater controls so used to tap the dash to get it working until one fine day when I tapped said dash to hard ( I thumped it) and activated the intertia switch at a T junction and promptly lost all power, after the AA had found intertia switch ( and showed me where the flaming thing was everything was a go again, soon got that connection sorted and didn’t attempt that again in a hurry,,, so they do work rather well!
Do they ever trip out on bumpy roads?Unsurprisingly inertia switches are designed for steel monoque chassis vehicles, development work and testing would have been conducted on a range of steel monocoque vehicles in various simulated crash situations. The inertia switch used by TVR was designed to trip in response to shock forces transmitted through a steel monocoque chassis, it most definitely was never designed for, or properly tested on, a vehicle with a tubular steel back bone chassis and a separate fiberglass body.
I recently completed an electric fuel pump conversion on a friends 1968 Porsche 912 and used the same inertia switch we are discussing here, I used it as an earth interrupter. In this installation I was careful to screw the inertia switch securely to the inside of the so called 'smuggler's box' a space designed for the rare air con option my friends car never came with. Ultimately this convenient steel paneled box shaped void is part of the vehicle's monocoque structure so in the event of an accident will be subject to transmitted shock sufficient to trip the switch exactly as designed.
This was an example of the correct installation of an inertia switch, and far superior to TVR's less than ideal idea of screwing it the underside of the shock absorbing fiberglass dash. Smacking the steel panels surrounding my Porsche 912 inertia switch installation firmly with a rubber mallet tripped the switch every time proving it will definitely cut the fuel supply should my friend be involved in a shunt, I'm afraid you really can't say the same about TVR's effort.
It's also worth pointing out my mate's 912 is on Webber carbs so the Facet electric fuel pump I selected and fitted runs at a mere 5psi and only needs to produce a relatively low volume of fuel to feed the carbs, a TVR Chimaera on the other hand uses a Bosch high pressure injection pump pushing a far greater volume of fuel at a much much higher pressure (regulated at the rail at 38psi!!!!).
There is therefore a far greater case for needing an inertia switch on the TVR, it's nice that TVR thought to fit one for safety, but as with all safety critical components its worse than useless if it's been installed in a way where it may... OR MAY NOT work when you need it most!
Steve_D said:
Only ever taken one inertia switch apart and that one worked with a ball bearing held onto contacts with a magnet.
Shock caused the ball to break free of the magnets. Pressing the button pushed the ball back onto its seat.
Steve
Sounds about right, my dad was an electro mechanical engineer back in the 60’s working on power stations,,, he’d have told me that too,,, Shock caused the ball to break free of the magnets. Pressing the button pushed the ball back onto its seat.
Steve
Thank the lord for people like Steve on here clearing up minor details that help us understand our cars.
Happy new year to all the Steve’s out there
ChimpOnGas said:
False activation is not common and even less likely on a TVR, inertia switches do need to experience quite a bit of transmitted shock load to trip them. If you understand the design principle, intended application, and development behind inertia switches it becomes obvious why TVR's idea of just screwing it to the underside of the fiberglass dash is seriously flawed, unlike a steel panel fiberglass is exceptionally good at absorbing shock.
Unsurprisingly inertia switches are designed for steel monoque chassis vehicles, development work and testing would have been conducted on a range of steel monocoque vehicles in various simulated crash situations. The inertia switch used by TVR was designed to trip in response to shock forces transmitted through a steel monocoque chassis, it most definitely was never designed for, or properly tested on, a vehicle with a tubular steel back bone chassis and a separate fiberglass body.
I recently completed an electric fuel pump conversion on a friends 1968 Porsche 912 and used the same inertia switch we are discussing here, I used it as an earth interrupter. In this installation I was careful to screw the inertia switch securely to the inside of the so called 'smuggler's box' a space designed for the rare air con option my friends car never came with. Ultimately this convenient steel paneled box shaped void is part of the vehicle's monocoque structure so in the event of an accident will be subject to transmitted shock sufficient to trip the switch exactly as designed.
This was an example of the correct installation of an inertia switch, and far superior to TVR's less than ideal idea of screwing it the underside of the shock absorbing fiberglass dash. Smacking the steel panels surrounding my Porsche 912 inertia switch installation firmly with a rubber mallet tripped the switch every time proving it will definitely cut the fuel supply should my friend be involved in a shunt, I'm afraid you really can't say the same about TVR's effort.
It's also worth pointing out my mate's 912 is on Webber carbs so the Facet electric fuel pump I selected and fitted runs at a mere 5psi and only needs to produce a relatively low volume of fuel to feed the carbs, a TVR Chimaera on the other hand uses a Bosch high pressure injection pump pushing a far greater volume of fuel at a much much higher pressure (regulated at the rail at 38psi!!!!).
There is therefore a far greater case for needing an inertia switch on the TVR, it's nice that TVR thought to fit one for safety, but as with all safety critical components its worse than useless if it's been installed in a way where it may... OR MAY NOT work when you need it most!
You can be so negative Unsurprisingly inertia switches are designed for steel monoque chassis vehicles, development work and testing would have been conducted on a range of steel monocoque vehicles in various simulated crash situations. The inertia switch used by TVR was designed to trip in response to shock forces transmitted through a steel monocoque chassis, it most definitely was never designed for, or properly tested on, a vehicle with a tubular steel back bone chassis and a separate fiberglass body.
I recently completed an electric fuel pump conversion on a friends 1968 Porsche 912 and used the same inertia switch we are discussing here, I used it as an earth interrupter. In this installation I was careful to screw the inertia switch securely to the inside of the so called 'smuggler's box' a space designed for the rare air con option my friends car never came with. Ultimately this convenient steel paneled box shaped void is part of the vehicle's monocoque structure so in the event of an accident will be subject to transmitted shock sufficient to trip the switch exactly as designed.
This was an example of the correct installation of an inertia switch, and far superior to TVR's less than ideal idea of screwing it the underside of the shock absorbing fiberglass dash. Smacking the steel panels surrounding my Porsche 912 inertia switch installation firmly with a rubber mallet tripped the switch every time proving it will definitely cut the fuel supply should my friend be involved in a shunt, I'm afraid you really can't say the same about TVR's effort.
It's also worth pointing out my mate's 912 is on Webber carbs so the Facet electric fuel pump I selected and fitted runs at a mere 5psi and only needs to produce a relatively low volume of fuel to feed the carbs, a TVR Chimaera on the other hand uses a Bosch high pressure injection pump pushing a far greater volume of fuel at a much much higher pressure (regulated at the rail at 38psi!!!!).
There is therefore a far greater case for needing an inertia switch on the TVR, it's nice that TVR thought to fit one for safety, but as with all safety critical components its worse than useless if it's been installed in a way where it may... OR MAY NOT work when you need it most!
Your probably right but if I whacked my dash with said rubber mallet i’m fairly sure that would trigger the switch, if it worked with my palm it might work with a sudden and crashing inpact,, which any Tvr owner would rather avoid, I always leave a safe braking distance which is not only good curtesy its good practice and something any light weight car owner should employ as the weight over the front wheels ain’t great being so far forward of engine base line.
It’s best not to find out if it works which I’m sure was normal thinking 25 years ago !?
Classic Chim said:
Not in my experience, in all fairness I was whacking the dash served me right !
Considering how hard they feel on bumpy roads if you have stiff springs and low profile tyres it’s a suprise they don’t activate more often, I’ve buckled a wheel and blown a tyre hitting a new pot hole one time and that was a heck of a thwack but the intertia switch was fine. I was stationary so that might have had something to do with it.
Now you’ve got me thinking how do they work, I’ve got Brembo brakes and did loads of tests until I was stopping on a sixpence from high speed which had the back wheels almost off the ground and a lot of G force.
Another quality item of on our Tvr we don’t praise enough
This is interesting, I wonder if the inertia switch fitted to your car is of the directional type. I think that the earlier inertia switches are directional and the latest ones are omnidirectional and this possibly explains why the latest type of inertia switches are bigger, the thing is I haven't fondled every inertia switch on the market so am not 100% sure about this served me right ! Considering how hard they feel on bumpy roads if you have stiff springs and low profile tyres it’s a suprise they don’t activate more often, I’ve buckled a wheel and blown a tyre hitting a new pot hole one time and that was a heck of a thwack but the intertia switch was fine. I was stationary so that might have had something to do with it.
Now you’ve got me thinking how do they work, I’ve got Brembo brakes and did loads of tests until I was stopping on a sixpence from high speed which had the back wheels almost off the ground and a lot of G force.
Another quality item of on our Tvr we don’t praise enough
Edited by Classic Chim on Friday 28th December 12:46
Classic Chim said:
Interesting term for handling electrical goodies there PP, you have a passion that’s for sure 
Yes I do have passion for electrical bits yet I doubt it betters the passion you and others have for TVRs, I didn't always have this passion, I used to smash suspect relays to bits with a hammer and fit new ones, I now gently undress any suspect relays and see if I can help them in working a little longer, my affection towards electrical components does seem to be paying off and I am also applying the same to my walk of life yet am careful about who I fondleTry giving your car a fondle on new years eve and wish her all the best, she might give you an extra 5 BHP
Cheers and all the best for the new year
Penelope Stopit said:
Yes I do have passion for electrical bits yet I doubt it betters the passion you and others have for TVRs, I didn't always have this passion, I used to smash suspect relays to bits with a hammer and fit new ones, I now gently undress any suspect relays and see if I can help them in working a little longer, my affection towards electrical components does seem to be paying off and I am also applying the same to my walk of life yet am careful about who I fondle
Try giving your car a fondle on new years eve and wish her all the best, she might give you an extra 5 BHP
Cheers and all the best for the new year
Dunno about fondle but some big heads will give me extra hp,,, not that I need it but it’s always nice to have.Try giving your car a fondle on new years eve and wish her all the best, she might give you an extra 5 BHP
Cheers and all the best for the new year
Happy new year to you too.
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