Gauge Issues

I have a 2003 Outback LS and am having different issues with the Gauges. I have only owned the boat about a month, so I am not sure how long/why these issues are happening.

First, the Voltage Gauge stops working completely when I turn on the Nav lights. I don't think it is a battery issue as the gauge works as expected except when I turn on the Nav lights it drops to nothing.

Second, only the large Gauges light up. All the small gauge stays dark. All gauges work as expected otherwise (except for the first issue above). The larger gauges don't appear to be replaced and look in the same condition as the smaller gauges. There is an aftermarket tower added with 4 speakers, is there any chance the light wiring to the small gauges were diverted to the speakers? I tried to track some of the wiring, but I'm not exactly an expert.

Any insight would be greatly appreciated.

I have the same boat.When I turn on the lights the fuel gauge drops to zero and the oil pressure gauge pegs.Its probally a ground issue but I dont worry about it.I dont use the lights very much.

Grounding issue. The voltmeter ground is floating which has a voltage applied to the ground wire from another source. Get a voltmeter and trace the circuit.