Quote Originally Posted by paps02 View Post
not true.

the relay would stop the current being sucked from the primary battery to support the secondary battery thus seperating the batteries to do there different tasks..

think of it as a turnstile at suncorp stadium. you are the current. you go through the turnstile. it only turns one way so you cannot come back out.

anyways thats the least of my problems now. for some reason when i took out the fuse to reset my ecu the sound system now thinks my front speakers are subs... tweeters should not play bass let me tell you that much.
Ah cool, didn't realise you were gonna have a changover relay. You're right there though, it will leave you with a battery to start the car. But then you are still only running the system off one battery, and it'll go flat until you start the car from the good battery. Won't be much good for the battery to flatten it/fully charge it/flatten it etc etc