Seat Leon MK4 (KL) 2023 UK RHD – Amplifier Power Cable Through Bulkhead/Firewall
Guide
Hi all,
Just a quick update to my previous post regarding running an amplifier power cable from the passenger side into the engine bay on a UK right-hand-drive Seat Leon MK4 (KL, 2023).
I recently installed a Vibe 65.4 amplifier using the plug-and-play setup shown in a
YouTube video from a German company that specialises in Seat Leon KL audio upgrades. The installation of the 65.4 was straightforward, and the Vibe 400.1 simply piggybacks from the 65.4 via the RCA/high-level output connections, so everything integrates nicely.
The challenge came when I needed to run a dedicated power cable through the firewall. After quite a bit of searching, removing panels and investigating, I finally found a route that worked. Hopefully this helps anyone attempting the same job.
Before You Start
A quick warning: before disconnecting the battery, make sure anything you may need access to is already open. Many modern cars have electrically operated locks and latches. For example, the Leon’s boot won’t open once the battery is disconnected.
Battery Removal
- Disconnect the negative terminal first and tape it up safely.
- Disconnect the positive terminal and tape that up too.
- Remove the top battery retaining bracket (10mm).
- Towards the front of the battery you’ll find a retaining plate secured by a long 13mm bolt. Remove the bolt and work the plate free.
- Remove the battery insulation sleeve (trust me, it just gets in the way).
- Between the positive and negative terminals you’ll find an additional connector. Release the grey locking tab and disconnect it.
- Pull the battery slightly towards you before lifting it out. It sits in guides and won’t lift straight out otherwise.
Be warned: the battery is heavy and mine had no carrying handles.
Passenger Side Trim Removal
Open the passenger door fully.
The airbag switch panel can be carefully pried away using a plastic trim tool. Do not disconnect itunless you have diagnostic equipment available, as it may trigger an airbag warning light.
I simply pulled the panel away and taped it to the windscreen to avoid strain on the wiring.
Behind this panel you’ll find:
- One Torx screw
- One plastic push-pin fastener
Remove both.
Lower Dash Panel
The lower footwell panel is held in place by:
- Three Torx screws at the front
- One rear retaining screw with a moulded handle
Remove these and lower the panel carefully.
There is a footwell light attached. Disconnect the two-pin connector by pressing the locking tab.
Glovebox Removal
The glovebox is secured by:
- Three screws along the bottom
- Three screws along the top edge (visible when opened)
- One additional screw on the left-hand side inside the glovebox
Support the glovebox while removing the final screws.
As it comes forward you’ll need to disconnect:
- The glovebox light connector
- The glovebox light switch connector
- Grip clip for the wire and taps to remove should be fairly easy to do.
Once disconnected, the glovebox can be completely removed.
Finding the Firewall Grommet
This is the bit everyone seems to struggle with.
Lay in the passenger footwell and look upwards towards the firewall.
Imagine a clock face:
The grommet is round, remember you are going to work between the 11 o’clock and 1 o’clock position on it.
You’ll see wiring passing through a soft, round rubber grommet.
Routing the Cable
- Using a small headed screwdriver Philips, flat, torx or even a sharp pointy thing
, carefully pierce the grommet.
- The material is very soft, almost balloon-like, and seals tightly around anything pushed through it.
- Insert something but reasonably rigid. I used a plastic chopstick.
- Push gently until resistance is felt.
- Adjust the angle by lifting up and continue carefully.
- Eventually you’ll feel the resistance disappear and the stick will just continue going.
At this point, go into the engine bay and look near the ECU area where the battery was situated.
You should see the end of the chopstick emerge.
Tape your power cable securely to the chopstick using cloth tape or duct tape and carefully pull it through.
Job done.
Final Tips
- Apply a suitable automotive grommet sealant around the cable to maintain a good weatherproof seal.
- Secure the cable with cable ties to prevent rattles or chafing.
- Take your time when pushing through the grommet. Small adjustments in angle make a huge difference.
- Once resistance disappears, around 20–25cm of push is usually enough for the guide stick (chopstick) to become visible in the engine bay.
I know this
guide is quite long, but I wanted to be as detailed as possible because I couldn’t find a clear explanation anywhere when I was doing mine.
Hopefully it saves someone a few hours of frustration!
Please let me know if you need
help!
