[sjlawr]

"I have the same problem my 99 gt mach 460 system is bassless also from all rear and front speakers and I installed an aftermarket head unit and is doing the same thing, I was told that by installing the new head unit it will bypass the amps but no difference."

If you installed the head unit and just plugged it in to the factory wiring harness, you will only get high end. I know because I tired it, and was highly disappointed. Ford routes high and low end seperatly out of the stock head unit, at least the did in my 01. My suggestion would be to run speaker wire from the new head unit directly to the speakers. To do that you will either have to buy new full range speakers to replace the 5X7s in the doors and back dash board, or you can buy component speakers with cross overs and replace the tweeters as well. You can also get new amps and do the same thing. Thats what I did on my 01 v6. I hope this helps.