90% chance it's the 12v battery. Many Volts sat for a long time before being sold, long enough to let the 12v battery drain too low to fully recover.
7.5% chance it's a poorly-connected ground.
2.5% chance there's an aftermarket accessory causing a ground loop or electrical interference.
7.5% chance it's a poorly-connected ground.
2.5% chance there's an aftermarket accessory causing a ground loop or electrical interference.