1988 740 Turbo

Three problems here.

The first, is with my antenna and radio. As it stood before the "accident" I had a broken antenna with a functioning motor. Every time I turned on the car I could hear the antenna motor turn on, as well when I turned off the car (the telescoping part of the antenna snapped off a while ago). One day while working on my stereo (there were no open wires or anything) I decided to press the antenna button considering I didn't need it at the time (it was the first time I ever pressed the buttom). The moment I pressed it, all my lights went dim and my radio shut off and has not worked since. Also, now I don't hear the antenna motor turning on. I checked the fuse for the radio and everything looked fine. Are there any other fuses I should check for? I couldn't find the antenna fuse off hand. Suggestions?

Second.
If any of you know about car stereos and amps that would be great. I installed a new stereo and amp (sony 2 channel amp to power my 12 inch subs) in my car. The first few days, the amp worked great. After like a week or so, the amp started to give me an "over current" error. I took it to Best Buy to get tested and they said it works perfectly. I tested my subwoofers and they still work great. I did a little research on the internet, and found out that maybe my amp isn't grounded right. So I made sure to get a thicker ground wire then the power wire, and I also made sure to scrap away the paint where the ground is. IT STILL DOESN"T WORK!!!! I measured the resistance between my ground and my battery to be basically 0 ohms. I don't understand the problem. If anyone could help with this that would be great

Final Problem
I replaced the oil, oil filter, air filter and spark plugs on my volvo. Following that I noticed that my car did not accelerate nearly as well as it did previously. I am wondering if the type of spark plugs I put in is that important. Are the original bosch spark plugs super fabulous, or is there probably another problem? I'm not really sure because I am the first person to ever do any real work on the car.