It sounds like your friend just hard wired your head unit into your TB. He should've have used one of the recommended harnesses to install it. I don't remember all the harness part numbers but someone else will chime in eventually.
Do not get a cap. Upgrade the battery under the hood. Do the Big 3. Increase your power and ground cables. If they still dim then add a second battery in the rear.
Do not get a cap. Upgrade the battery under the hood. Do the Big 3. Increase your power and ground cables. If they still dim then add a second battery in the rear.
