I have the problem with the 95 sc400 nak radio, cd and tape skipping at high volume due possibly amp going bad.
took it to a car stereo shop and they said to check the ground wire to the amp probably needs cleaned and it should be grounded close to the amp location.
Well i took out the amp and didn't find any ground wires just three connector plugs to the amp nor water in the trunk, does anyone know were the amp grounds out at?

 

I have the same issue with my Nak system.
Haven't found out what the source of the trouble is....

 

All the searching points to the amp.. Someone has to know a solution.