That fuse is a surface mounted fuse and is very small and hard to locate on the main board of the radio. If you have a Pioneer head unit, I have seen many of them with an open ground fuse for the RCA jack. You will then need to have the head unit serviced. Any voltage here will cause the amplifier to go into protect mode, which is what is happening to you. Do the same for the other channel as well. With the RCA cable disconnected put the red lead on the inner part of the RCA cable and see if there is any DC voltage and then check the ground or outer part of the cable. Take the black lead and make sure it is grounded to the chassis of the car or to the ground of the power terminal, be careful and make sure it does not touch anything else. Set the meter for DC and for a max level of more than 12 volts.

If you have a voltage meter, you can use it to find out very quickly. You need to figure out if the problem is coming from the head unit or if it is in the amplifier.

It sounds like you have some DC voltage on the RCA input.

Power acoustik pd 931nbt