Not my car but Steph's Coupe.
Her sub ran fine in the fiesta until she replaced her head unit. We put it down to a bad earth on the sub. Weve now transferred the system into her coupe and are having the same problem.
When the stereo is down low the sub works. However when the volume is turned up the sub is fading on the power light. Iv cheked the earth, remote and power cables and all are fine. The battery and the alternator have been checked on the car and that's ok too.
I can't for the life of me working out what it is going on with it now. Could it be to do with the headunit's preouts being 4v as opposed to the old radio (which the sub was connected to previously and ran fine on) only being 3v.
The only thing i can think of is that her headunit is somehow faulty.
Any information/suggestions will be much appreciated as this is driving me round the bend as im getting moaned at to fix it!