Ok i bought car 2 weeks ago a 99 civic si. The cd player in car on way back home from getting it shut off and wouldn't come back on. The next day it would turn off and on, over and over again. So i took what crappy system he had in car out. and i got new cd player and 2 new front speakers and still having problem, my new cd player goes off and on over and over again. Seems to be after car warms up??

I am stomp on this, i have checked my wires and took out all the wires he had runned for amp and sub's and still doing it?

 

faulty alternator/bad battery is a potential problem. check voltage from power wire key on engine off should be battery voltage. does it do it when the car is off or only running? if only running then i'd suspect alternator. if off and running then check fusebox for a short or some crappy wiring job to the radio harness.

 

Only will cut off while driving, i just took it out a hour ago. Worked flawless for first 20 mins or so. With heat on and headlights. then shut off so i pulled over and trying using any power options on car and opening doors, nothing. turned off and back on nothing. So i drive all way back home with no radio and pull in my garage and still couldnt get it on. So i pop hood and open fuse box under hood and pull out the 7.5 fuse for radio (still good) put it back in and then i got radio to come on without the car on.

It seems to play as long as i want with car off, but once i start driving it seems to last like 20 mins before it starts acting up. Will just shut off and power itself back on sometime over and over again..

 

so when it shut off you also didn't have any other power options? windows, sunroof, door locks? definitely a short and possibly a relay starting to go bad. i'd start by idling it for 17-18 minutes since you know it works fine for 20 minutes then pull the fuse out and test voltage at the fusebox and see if power is getting lost there. if you still have power then you can narrow it down to the radio harness but i'm curious what other options run off that same circuit since you said other ones wouldn't work.

if no other power options work when the radio cuts out then it has to be something that feeds power to the fusebox that is cutting out. i believe your car has multiple relays/fuses that feed power from the underhood fusebox to the under dash fusebox. start with the diagram that tells you what fuses/relays control what options and trace back to look for any breaks. also if some options work but others don't and since we know fuses can only blow once then i'd take known good relays and swap them with questionable ones and then test drive again.

 

No all my power options work flawless. Windows, mirror's, sunroof, lights. Everything. Just radio giving me problems. And i have let it run for awhile seems to work fine sitting still, but maybe i will time it next time to see.. But when i turn on lights it dims my light on my head unit (but figured that was normal since civic seem to be loaded down with power options..