Nav. lights shorting out

[sullmate]

When I push the toggle switch to the anchor light side it works fine. When I put the toggle to the nav light/anchor side the anchor light shuts off and the front light bulb burns dimly. Eventually the fuse blows. How should i go about diagnosing this problem. The wires from the front and anchor lights end up going to a large wiring harness. Thanks for your help.

 

[joeanna]

I'd start with checking the nav lights first,(connections,socket...)it may be really corroded causing a short making that one appear dim and the other not getting enough amps to even light up, then I would check the toggle ( same check), then the harness.