Mazda Repair: shortage, negative battery cable, mazda 626

Question
I have a 1998 mazda 626.  My son and his friend were attempting to connect a stereo and amp when suddenly the stereo had no power and the inside light on the car died.  they were going to pull it up under the carport and when they put the car in reverse it dies.  you can get it to restart but only by jiggling the negative battery cable.  every time you put the car in evers ( even if just going thru reverse to get to drive) the car dies and will turn over but not fire uness you jiggle the neg cable.  The car will start in nuetral and go to drive with no problem, but if you try reverse it dies.  please help this confused old man help his son.

Answer
Replace negative battery cable, clean all the connections.
If he is using a power cap, remove it. If he has run direct wiring from the battery to the amp disconnects it from the battery and have them install the correct adapter terminals for installing amp cables to the battery.

The reason it is dying is the negative power lead is not getting enough of a contact to run the amp and the car at the same time. Try the cables and cleaning and then get back to me and we will go from their.

Regards,


John