Can i play music through my iphone4 into the front usb on my jvc kd g646?

It is due to the bad connection to the battery or your battery can be weak and also check all the connections sometimes loose connections can cause sound, a weird sound.

You might have to reset the logic by disconnecting the power to the unit. Remove the fuse temporarily, or both fuses if it has 2.

It looks like the JVC will control the iPhone as a music player through the USB. However, unless the YouTube app or another app can give you that same control, the simple answer is to use an aux cable (3.5mm stereo/headphone jack on both ends). The problem with this solution is you will have to select your videos and/or music through the phone. Unless you have a YouTube playlist set up, I would not recommend you do this while driving.

If it was working before and no changes made to wiring, then it needs service.

When Connecting Smart Items like Apple Stuff to JVC the DEVICE provides the JVC with the music. You cannot drive the Apple Device through JVC remote or front Buttons.

run an earth wire direct from the battery to the stereo

If it is a "Ready for BlueTooth" model you will need this adapter JVC KS-BTA20

You are connecting it to a car DVD player, but how many types of music format is it capable of playing? It should be in the Manual, however it will be able to play mp3. *.flac, *.wmv, *.wav, *.cda. But how ere you going to power your external hard disk? If it has provision for use of 12V DC voltage, same as that of the car. After its powered, only then will it work, but the USB connector will provide the output into the DVD players USB slot(just like attaching a flas drive like pen drive which uses the USB slot for power too....sodeep

You can use any non powered USB drive (gains its power from usb only). You just have to plug it into your PC and select Properties > Format then make sure you format it in FAT12, 16 or most commonly (recommended) FAT32 file system.

Once you've done this you can transfer all your music onto it then plug it into the USB port lead from the back of the head unit

Good morning (jhb 8:20 am)

I thank you for the quick response regarding my JVC KD-DV7401 not picking up the USB 'source' I managed by using a different brand and it worked, although it seems like it don't work with different types of music folders/formats so I need to figure that one I'll be more than happy.

Regards
Cleavon