Add inertia switch to 1s?


i would add an inertia switch to 1 s ,

Someone have already add ?

what you think about my idea?


I think it is a good idea. I bought one (Series 3) to add about 30 years ago. Will get it done soon. Time flies (an English language expression that means “I move very slowly”). :slight_smile:

No rush then Robert :slight_smile:

OK, I’ll ask, what’s it do gents?

In newer cars when involved in an accident it cuts off electrical power to the fuel pumps and possible unlocks the doors, not completely positive about the last part.

Thanks, so for extreme inertial situations! Paul

The Series III XJ6s and XJ12s as well as the XJ-S/XJS all have an inertia switch as a safety enhancement that shuts off electrical power to the fuel pump in case of an accident. In some models it also disables other systems. This prevents fuel being pumped after an accident to prevent or reduce fires.


The inertia switch, originally installed, Fred - effectively cuts power on all white wires when an impact is detected, killing ignition, fuel pump and ECU. It is an additional safety feature to the reed switch in the EFI that prevents the pump running with the engine stationary and ign ‘on’ - overridden in ‘crank’…

On carbed engine; a fuel safety relay performed the latter function - after a crash , having the fuel pump running is ‘counterproductive’, and there is no need for ignition either…:slight_smile:

Basically, the safety devises has the effect of turning the ign key to ‘off’ - without the need for driver action…

xj6 85 Sov Europe (UK/NZ)

Thank’you all.

Last sundey a crash here…
during a classic car meeting…

So , now all here tell about this switch.

They have all same tecnology?

old switch come from s2/3 or a 2019 product is best choice?

thank you.


If it works it will do just fine.

Decades ago, I was driving my 88 T Bird along a fast moving freeway. Wham, I got it along the left rear, pretty hard. The car shut down!! Luckily only one lane to cross to get to the shoulder and safety… I coasted over and stopped. The little truck that hit me pulled in behind. A true gentleman, perhaps not so wise, though Fessed up and apologized. We agreed to call the CHP.
Good guy, the cop. got the info, did hs notes for the report, etc. and offered help. I had an inkling as to inertia switches!! But, on this car, where ?? I got out the driver manual and found it. In the trunk/ boot. Pulled away a bit of trim and there it was. punched it. got in the car. Cranked. Cop with hand on the hood/bonnet. Two thumbs up!! cop said" I have Musatng,. same platform, just learned a couple of things, put eh manual in the car"!!!


I was in a friends X300 going to a committee meeting a few years ago and in the outside lane of the motorway we felt a small bump and the car lost all power, yep the inertia switch had tripped. Neither of us could find the damned thing, ended up calling the AA (AAA to the yanks) and even he had a lot of trouble finding it. Luckily another member came along and I was able to leave the owner to continue to the meeting.

All such inertia switches works the same way, Fred - breaks connections when bumped…

The drawback is that you may not want to lose engine power after a bump. Turning off the ignition is just as effective - if you are still conscious…

xj6 85 Sov Europe (UK/NZ)

Aye to the last.

And also, there are some that lack the presence of mind to turn off the switch!!!

Factory “fail safe”…


Ok will be in center consolle next fuses,i will add a photo here!