Here’s pictures of the hu wiring it may vary to what’s in your friends car I can take more tomorrow if you want pictures of the actual inputs on back of the stereo. depending what your friend has installed it’ll be different my rcas just go into back of head unit if they have a standard headunit you’ll need to use a line out converter connected to rear speaker wires to use rca leads instead of plugging rca’s into the hu also the same if the amp has high level inputs if I’m correct I’m not really familiar with that way as I’ve never done it probably best to ask xplaya. Also another note if your friend has an aftermarket alarm system make sure he disarms it using the siren key before disconnecting the battery for the amp power wire / fuse or the alarm will go off I nearly forgot to turn my alarm off using the key my neighbours wouldn’t of been happy I like in a block of units lol.