Installing fuel pump kill switch but don't know which wire

[Sinnedstone]

Hello all,

greetings from Vilnius Lithuania -2020 EB owner.

Question:

I'll be doing a roadtrip through Europe this August and I want to install a kill switch. I will actually have a can bus immobilizer installed but the company doing it is booked full till mid August. As I will be driving through Italy, Czech, Hungary etc. I want to have at least something to make it more difficult for any carthief as here in Europe these Mustangs stick out.

I want to place a kill switch on the Fuel pump as it's most easy to install and I can route it somewhere in the boot, it's pretty straight forward. The only thing I am struggling with is which cable to use. Is there anyone here that can tell me which cable I have to cut and put the switch in? I read somewhere that one can also pick the groundwire, call me a noob but, electrics don't need a ground wire to be switched on....right? Anyway, pics attached, if anyone could tell me would be much appreciated.

Thanks!

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[Coyote Chase]

Looks like the small wires go to the sending unit and the larger wires are for the pump motor. If I had to make a guess... I'd probably install the switch in the big yellow wire.
However, I don't like to guess!

 

[Sinnedstone]

Looks like the small wires go to the sending unit and the larger wires are for the pump motor. If I had to make a guess... I'd probably install the switch in the big yellow wire.
However, I don't like to guess!

Many thanks for your input, I think the thick yellow/grey wire is the trigger - so that should make it the one to cut (I suppose)

 

[Sinnedstone]

so I went ahead and connected the switch to the yellow/grey wire - turns out it's a ground wire, as the car would even start with one of the leads disconnected. I waited to be sure all the fuel would have been out of the system but it kept idling. Now I have a check engine light which, hopefully will go away. Anyways, not the yellow grey wire LOL .....

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