amp, not working after swap

Just recently attempted to put a different amp into a friends car to test to see  how the amp worked. Took the wiring from the existing amp and hooked it into the other amp. The amp was apparently blown as it did not turn on or show any signs of life. Not a big deal. However when i attempted to re-install the friends amp that had worked in the car before installing the busted amp, we hooked all of the wiring up turned on the car with the volume at zero and  the subwoofer went crazy. we shut off the car and wired and re-wired the amp making sure we did not pinch any wiring somewhere. I am new to installing and am at a loss as to what to do, one of my friends told me to check the ground wire. Any ideas?

Your friend has a Pioneer radio. You did not follow the first rule of car audio installation, which is disconnecting the battery of the vehicle before performing any work on the stereo system.   Sometime during the amp swap there was power and RCA connected to an amp before ground was connected to it. When the power wire is connected to the amp it starts looking for a ground, an amp does not care where it gets ground, it is looking for the first available. The RCA jack of your radio is a ground. Well, it was until the amp found it. The amp pulls plenty of current and takes a large power and ground wire. The RCA cable and the ground path of that cable inside the radio, not so much a big wire or big traces (in your case a tiny surface mount fuse) inside his radio. Hope you are still reading this. I know it is long but here is the help you were looking for. Since I do not know what model Pioneer radio he has, I can not tell you exactly where the fuse is located. So the following is a generic fix for your problem.

https://bcae1.com/images/rca/temporaryrcashieldrepair.html

The only other thing that could have caused this, would be the power wire of the amp touching the shield of the RCA cable.  If you are looking for a simpler fix, you could just strip back a few inches of wire and wrap it around the shield of the RCA cable, then ground the other end of it.  I don't know how long it will work for you, but without the solder I guess that it will be simpler.

can you tell me where i could find the fuses and the holder that are shown in the picture . is that something the a best buy or circuit city would carry or should i go to like an autozone?

Any small fuse holder will work. Autozone, RadioShack, PepBoys. doesn't really matter.

okay thanks for the help i'll give it a try

To make it simpler yet, you only need 1 fuse holder and you only have to do one RCA cable. Left or right, it doesn't matter which one you do.

even better

Some amplifiers depend on the ground of the RCA jacks to get a ground reference. Some amps have the shield of the RCAs grounded inside the amp. Chances are the amp you just put in does not require ground on the RCAs. So down the road when you get a different amp, you will probably have the problem again.

oh. well that explains it. could there be something that goes wrong down the line with this amp if i do not ground the rca's ? I dont want to take for granted that the system is playing now and cause further damage to something else

If it is playing fine now then there is nothing to worry about.