your tape probably has 2 RCA outputs. but your amplifier has 4 RCA inputs. The way to make the tape with 4 outputs is to buy Y chips. here is the picture:
the single end will be attached to the tape, and the double end to the CH1 and CH2 in Low Input. that is, the white RCA cable of the tape will be connected to CH1 and CH2, and the red RCA output to CH3 and CH4. so you need 2 of these Y chips. (pair 7-8 TL)
There are already 4 speaker outputs in the amphitheater. The cable ends of the speakers will be connected to the screws under the Speaker inscription, corresponding to each cable (+) and (-).
audio cables input and output processes are finished ... in the electrical installation ...
There are 3 screws under the POWER post.
GND: the chassis, that is, the negative end. The cable to be connected to any iron parts of the vehicle will be connected to this GND end. For example, the seat belt under the rear seat can be taken from the fastening screw.
REM: The blue cable on the back of the tape will be extended and connected here. There is already 1 blue tip on the tape. this cable also turns off the amplifier when the tape is turned off, and turns on the amplifier when the tape is turned on.
BATT: (+) is the end. A fuse in the picture below will be mounted on the cable from the positive pole of the battery. it's pretty simple. then the tip coming out of the fuse will be connected to this BATT screw.
electrical connection is also completed. You can adjust the location of the fuse according to your head. they usually install the fuse somewhere next to the battery. The (+) cable from the battery should be as thick as possible. it may even be as thick as our little finger.
I tried to explain as much as I can, let my friends fix it if I am wrong, I am waiting for questions if there is a place that is not understood. Good luck with.