[Head_Shaker]

New to me 06 39 convertible,  2 fresh water pump breakers, when running shower or cockpit wash downswater 
 breaker pops when both breakers are on. Replaced shower box float and flo jet pump, also get a pulsing on all lights on boat when running galley sink?  Any suggestions on what is going on?  Thanks for any help, this is driving me nuts! Cristina

Sounds like you have low batteries on the house side and when you are running the freshwater pump it is drawing enough amperage to make the lights dim and breaker pop if the draw is too great.

When you are hooked up to shore power and shore water, with your freshwater pump turned off on the panel does the issue still exist? 

OR - 

Without being hooked up to shore water but being on shorepower with your battery charger on in the panel and freshwater pump on in the panel does it still happen? If it doesn’t that helps identify low batteries, since when on the charger it should for a short term keep the lights from dimming even for a little bit till the amperage draws down. 

Just my thoughts to start to try to diagnose it, how old are your batteries, if newer you could have a bad cell causing issues and then lastly it could be a short or bad ground someplace which would pop breakers and also fuses if so equipped.