No power to ignition switch but central locking works fine - Octavia II BKC

Hi everyone,

I have a 2006 Skoda Octavia II, 1.9 TDI, engine code BKC, around 400,000 km.

Symptoms:

- Central locking works perfectly fine (all doors lock/unlock with both remote and key)

- The trip computer/dashboard display works normally - shows mileage, trip info, and door-open warning

- However, when I turn the ignition key, NO ignition warning lights come on (no battery light, no oil light, etc.) and the starter motor does not engage at all - completely dead on ignition

Important context:

- The wiring harness has previously been tampered with by a previous owner or mechanic (unknown extent of modifications)

- An auto electrician was probing around the fuse box area with a test light trying to diagnose the no-power issue. During this, the power flickered on and off a few times while he was probing - suggesting it might be a loose connection or bad contact somewhere rather than a fully severed wire, since touching/moving things briefly restored power.

What I've already checked:

- Battery voltage is fine (~12.4V resting)

- Central locking fuse is OK

Other known issues on the car (in case related):

- P3101 fault code (intake manifold flap motor - open circuit/short to ground)

- P0299 fault code (turbo underboost)

- These were read while the car was in limp mode

Based on the above, it seems like terminal 30 (permanent power) and ground are fine since the trip computer and central locking work, but terminal 15 (ignition-switched power) seems completely dead - no dash lights, no starter.

My questions:

1. Where is the terminal 15 fuse located for this model, and what is it usually labeled as?

2. Given that power flickered when probing near the fuse box, could this suggest a loose fuse, corroded fuse box contact, or a bad connector/splice nearby?

3. Could this point to a faulty ignition switch itself, or is the immobilizer/comfort control module more likely when there's a complete absence of terminal 15 power?

4. Given the wiring has been tampered with, are there common splice points or relay locations for terminal 15 that are known to fail or get disconnected on this model?

I have a multimeter and am comfortable doing basic voltage/continuity checks if someone can point me toward the right connectors/pins to test.

Any guidance would be greatly appreciated. Thanks in advance!