I had an aftermarket SONY radio-cassette installed by the previous owner. When I replaced the dash last year, I had to go through a maze of aftermarket wiring for the stereo and the alarm. It was not fun.
You are going to look for three connectors. One front speaker connector, one rear speaker connector and one power connector It usually will have grey, black and yellow wires. Don't recall the color of the fourth. The speaker connectors are blue and white.
Your unit must have three slots in the back plus a fourth connector that is independently in the same rear panel. That one powers up the digital clock of the audio unit, possibly using the pink wire connector you pictured, or an orange wired one. Good luck.