Ground for amp on 170

[Romieroo]

Someone gifted me a Bluetooth speaker setup with an amp but it says to wire the amp to the ground. I only have the old switch and fuse setup on my 170. What can I wire it to for a ground? This will share a battery with VHF and GPS/fish finder

 

[Dave LeGear]

I recommend checking here first:

https://www.performanceoutdoors.net/forums/general-marine-wiring-related.130/

And look / use the same color and wire (they) denote for the current ground wire for the boat present harness.

https://www.pacergroup.net/abyc-color-code-standards/

Don't try and reinvent the wheel, just ride on the present one