Radio/Speakers problem

[Wisha Haddan H3]

The first thing I'd check is the electrical contacts. If they're loose or dirty, that increases resistance to the speaker, which requires more current (higher volume) to overcome.

Don't know how it was installed, but if you didn't use a factory harness adapter, make sure all connections are clean, sautered and shrink-wrapped. Don't trust electrical tape or wire nuts in vehicle installations. Tape melts and fouls the connection. Wire nuts vibrate loose and have higher electrical resistance. Some swear by crimp connections, but I don't like them. Even with a sleeve, they're vulnerable to dirt and condensation.

Here's a short guide to 12v electrical splices

If you do have electrical tape somewhere, clean the wires off with rubbing alcohol and brighten them with steel wool (cut and strip to new copper if you have to). Then solder and use a shrink sleeve when you re-splice.

Good luck finding the problem