Inside upgrade extension cable Focal's Inside system upgrades include new aftermarket vehicle-specific speakers and subs, along with their Impulse 4.320 4-channel amp. Focal also offers a variety of cables and connectors that you'll need, including: speaker wire harnesses for tweeters, subs, and center channel; T-harnesses that connect the vehicle and factory radio to the upgrade system; and extension cables to connect the T-harness or factory radio harness to the amplifier. This 5-foot extension cable connects an Inside upgrade system's vehicle-specific T-harness or your vehicle's factory radio harness to a Focal Impulse 4.320 four-channel amplifier.