Battery voltage drops when high amps needed for horn and halogen lights?

[Bustedknuckle84]

2002 Cape Craft, with 03 Honda 200hp. I'm experiencing a recent issue where when I try to turn on my deck halogen lights, or use my horn for example the voltage is dropping significantly. The lights, radio, and stereo are on a different wire than the horn wire. Regardless, I have good batteries, and just replaced my boat horn.

Heres the deal. The newest battery (less than yr old) will measure 12.68 at the source. When I measure the voltage to the main Glass Fuse Block it drops to 12.4. My GPS, nav lights, bilge, aerators, etc work fine. Engine turns over fine.

When I hook my gauge up to the ground and positive wires to the wires going to the horn and press my switch(button) the voltage drops to below to 4-8volts and horn doesnt work it attempts but makes a weak boop and thats it.

When I disconnect the power wire to the horn and press the switch, it reads 12.4 volts.

It seems like the voltage is going to the horn and halogen deck lights correctly, but the amp draw of them drains the voltage to where they don't correctly function.

What should I look into?

 

[Scott Danforth]

Clean your contacts connections, etc. What you are describing is a dirty connection

 

[GA_Boater]

If you only changed the horn and it all worked before, I know where I would start.

 

[Bustedknuckle84]

thank you, just for those 2 sources or should I be checking something else as well?

 

[Scott Danforth]

I would start at the battery(s) and clean every connection so it is shiny and clean enough to eat off of. work your way all the way up to the ground buss under the helm.

then when you are done, seal all the connections with marine electrical varnish