Thought this would be a simple task (done it before on a 1998 Peugeot Boxer and a Citroen BX) but wanted to make sure I didn't fry anything so wondered if anyone had done something similar - I'm working on a 2007 Ducato 100?

I'm looking at layered security here, and doing it for a bit of fun/education!

I've bought the relays (circuit taken from the12volt dot com relaydiagram12 - can't post the url as I've not posted enough times yet) and created a test circuit and I'm happy it all works. The problem I'm having is choosing a suitable circuit to cut for the relays to re-connect, I'd prefer not to run a wire from the engine bay (more work but happy to do it if that's the way to go) so was looking for a suitable circuit to interrupt. Removing fuse 42 (ABS, ASR, ESP, Brake light control) stops the van starting but after speaking to a car mechanic he thought this might upset the ECU if I cut interrupted it.

Ideally I'd like to cut a feed to the starter motor relay but looking at the downloaded manual I can't seem to find it. I thought it was connected to fuse 31/38 according to the manual but taking those fuses out didn't stop the engine starting.

Has anyone fitted something similar, or have any thoughts on a suitable circuit to cut that is easy(ish) to get too in the cab?

Thanks
Mark