Some VHF radios have an in-line fuse.It will be on the red (hot) wire.Sometimes the silver ends of the fuse or fuse holder will get corroded.This can cause a drop in the voltage to the radio.They are spring loaded and be sure the spring puts tension on the fuse.A very light sanding with emory cloth will clean the ends up like new :thumbup:.
It took me 2 hours to track down this gremlin on a friend's boat :eek2:.Drove us nuts trying to figure it out.
Also check if the radio wires have a push/pull connector - these can also be corroded.They often look fine on the outside but once apart reveal green.
FYI: Be sure to use marine grade (tinned) wire and the proper marine heat shrink eyes and butt connectors.They are expensive but do a great job. Boaters World carries a good selection :thumbup:. Using regular wire and electric tape does not hold up very well on a boat.