97 cavalier problems

I have 2 problems as of right now. The first is a power loss when I apply the brake. Occasionally the lights will dim and the radio will drop out. It may be due to the fact that I have an 800 watt amp hooked up, do I need to buy a bigger alternator, or is it something else?
The second problem is a squeaking noise when I turn the wheel or hit a bump. It had this problem when I bought it, but when I went through the recall on the rack and pinion gear it stopped. Despite the fact that I have new struts it recently started again. What could cause this? Any information would be greatly appreciated.

sound like loose connection check battary cables starter wires and body ground wire
you do not need high amp alt