running two car batteries

i was wondering how to hook up to car batteries in my car i need to rn two b/c the one i have the head lights dim and i have a cap.  do u have to have a battery isolater to hook up two batteries or is there a better way to do it.  ive tried two battery isolaters and neither of them have worked.  you input would be greatly tanked so i can get my system back up and running. 

try have the alternator rewound to HO at a local rebuild shop. if the alternator isnt big enough to produce enough power to 2 batteries then it wont do ant good.

the alternator is plenty big to charge two batteries i just need to know how to run the wires

OK, slick... 1: Just wire them in parallel. Forget any isolation techniques - this means solid-state diode types and relay types... leave them at the PepBoys accessory desk. I will not go any further with that - just don't use them... If you want to read further, check out this thread... 2: Dual batteries will do you NO GOOD WHATSOEVER without an alternator large enough to power the entire car as though there were NO batteries in it. Your amplifiers do not run off the batteries, they run off the power produced by the alternator. Get an HO alternator, before you go spending money on a second battery. If you ask again, you will get the SAME answer from everybody that knows what they are talking about on this board.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."