Originally Posted by
David Analog
David,
A couple of thoughts.
I think I read about the HU power and ground. But the HU has two powers, one constant, and one switched. Both powers should access the same physical point, at least during diagnostics.
The HU should be totally disconnected from any previous or existing dash ground whether that be through the harness or chassis.
Switching the lighting module from the dash is convenient. But I would have the dash switch control a relay and source both the lighting module positive and ground directly to the non-stereo cranking battery, and fuse the positive side at the source. I don't like bypassing the battery switch but this might be helpful with RGB lighting.
I would ground the factory helm ground buss on the cranking battery. Double check that all factory grounds are very well secured.
Batteries should be fully charged.
All gains should be properly set.
Experiment with EQ internal ground reference per MLA.
Verify whether or not you have alternator whine upon starting the engine.
There's more to the diagnosis process, but it would help to eliminate the above potential causes. This is a good start.