I installed a new Custom Autosound USA-740 this week and with key-on/engine off it plays beautifully at any volume range.


with engine on though, the radio seems to be going into a protection mode, with the volume level dropping and rising in continual repetition. Turning volume up only causes distortion and the volume fluctuation continues unabated.


I swapped speakers for comparison, no change in the condition. Only running a set of Memphis Audio 6.5" coaxial kick panel speakers (4ohm).


I wired the stereo (+) lead into my original radio connector within the dash harness, grounded the (-) through the firewall to a 12g wire connected to chassis under hood. The memory lead is connected to a full time (+) as required for station retention. No pinched/chafed wiring.


Power lead measures approx. 12.2v in key on position, 14.2v+ with engine running. I'm not hearing any ignition noise/whine through the speakers with engine on. Volts are solid at the power lead with engine on, even as the volume level continues to fluctuate up/down.


So I'm wondering if there's something wrong with the radio circuitry that is forcing it into a protection mode with the engine on, i.e. is it failing to operate properly at the running voltage level (14v+)?


Or is there potentially some kind of electrical interference filtering through the wiring that's triggering the issue?


Only running the radio and 2 front speakers - no separate amps or subs.


I plan to contact CA tech next week but hoping I can find a solution over the weekend.