Symptoms
- Battery dies overnight after installing a new stereo or accessory
- Stereo or accessory stays on or lit up with the car off
- Battery drain started right after an aftermarket install
- Clock or memory settings reset frequently
Likely causes
- CommonAccessory wired to constant power instead of switched powerWiring meant to only be on with the ignition can be mistakenly connected to always-on power.
- CommonAmplifier remote turn-on wire miswiredAn amp that doesn't fully power down can pull a small but steady drain.
- PossiblePoor quality or loose aftermarket wiringCheap connectors or splices can create a partial short or drain.
- PossibleAlarm or dash cam left in an always-recording modeSome devices have parking modes that draw continuous power if not configured correctly.
What to do
- Check if the aftermarket device has any lights, displays, or sounds active with the car off.
- Review the installation to see if power wires were connected to constant (battery) power versus switched (ignition) power.
- Disconnect the aftermarket accessory temporarily and see if the overnight drain stops.
- Check any parking mode or always-on settings in dash cams or alarms and adjust or disable them.
- Have the specific wiring re-checked by whoever installed it, or a mobile installer if you didn't do it yourself.
- Test the battery and charging system to confirm they're healthy once the accessory issue is addressed.
- Consider adding a dedicated switch to manually cut power to the accessory when parked long term.
- Avoid running high-draw accessories directly off the battery without a proper fuse and relay setup.
Tools and parts
- Multimeter (for testing drain)
- Wiring diagram for the accessory
Add-a-circuit fuse tap (for proper switched power)Search: “add-a-circuit fuse tap kit”
When to call a pro
If you're not confident tracing wiring on an aftermarket install, a mobile car audio installer can quickly find and correct a wiring mistake.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.