[Robert Gift]

Where can I cut in a hidden switch to prevent an Expedition from being started and stolen?
This is an emergency medical vehicle with an extra key hidden in the vehicle interior.
We would use the door code to get in if our keys are lost in the middle of the night.
This would be an added safety feature.

Thank you.

Robert

[CaptainRich]

Since the Powertrain Control Module (PCM) controls power to the fuel pump, an interruption there could potentially cause a check engine light.
Actually, that could happen almost anyway since the PCM will look for results after applying power.
What you might try is controlling power to the fuel pump relay.
That is a twenty (20) amp circuit so the switching device must be capable of handling that amperage.
Who will be installing such device?

[TxGreaseMonkey]

I like CaptainRich's suggestion of controlling power to the fuel pump relay a lot. Normally, Ford locates the fuel pump fuse and the fuel pump relay in the under hood fuse/relay box. In a pinch, you could just remove the fuel pump fuse.

[Robert Gift]

Since the Powertrain Control Module (PCM) controls power to the fuel pump, an interruption there could potentially cause a check engine light.
Actually, that could happen almost anyway since the PCM will look for results after applying power.
What you might try is controlling power to the fuel pump relay.
That is a twenty (20) amp circuit so the switching device must be capable of handling that amperage.
Who will be installing such device?

Thank you, Captain.
I would be doing all the work.
Yes, I was thinking of connecting to a fuse which I can moreasily access.
A switch can be installed in the siren and lights controller but not sure if a 20-amp switch can fit.

Can I cut a wire from the ignition switch (if I can find it) to a lower amperage switch?

Thank you.

[Robert Gift]

I like CaptainRich's suggestion of controlling power to the fuel pump relay a lot. Normally, Ford locates the fuel pump fuse and the fuel pump relay in the under hood fuse/relay box. In a pinch, you could just remove the fuel pump fuse.

Thanks, TX.
When entering/exiting the vehicle we're in a hurry so a switch would be best.
Placed in the siren unit, no one would suspect the switch enabled the vehicle to start. (I could use a SPDT so the wrong direction sounds the siren!)
I'll go look for that fuse. Would a Zip cord carry enough amps to allow the relay to work OK?
If one operates the ignition without the relay switch closed, would that cause a permanent Check Engine lighthat would need to be reset?

At 3 a.m. I can see myself forgetting.

Another thought would be to place the switch in the fuel inertia switch circuit - if I can find the wires to that.

Thank you.