I'm installing JVC CD Receiver into Hyundai Accent instead of the original radio. I did all wiring from the receiver to the wiring kit-plug (but just tying it using the heating tubes, without solding) that should connect the receiver to the former radio plug. When any three speakers are connected it's working well. But, when I'm connecting any fourth one there is a noise with turning sound up. The previous radio sound was perfect for all four speakers with any high volume.

I changed the wiring kit thinking that something wrong with wires but now there is a noise even with any three connected speakers.

Could anybody advise anything?

Thanks

I assume the connections(all 8, 4+ and 4-) are connected with correct polarity?? With the wire harness of course they are, so honestly man I'm thinking it's the deck!! For all the work you are doing with the heat shrink, if the car is just adding a cd player to it and not competing or anything just undo the speaker connections and try again but dont heat shrink the connections this time, use electrical tape!!, as you make each speaker connection turn on power and check for proper sound from that speaker before you do the next speaker. If you still got noise, like I said the deck , or try not using the factroy ground wire and make a new one!! I hope this helps!!

A lot of cars are coming with 2 ohm speakers these days, that way they don't need a big power supply for the amp.
Most aftermarket head units will drive 2, 2 ohm speakers or 4, 4 ohm speakers.
So, if you haven't changed the speakers, you probably can't run 4 off the deck.