The breakers are mostly either in the main panel next to the galley, or in the panel in the engine room on the aft bulkhead.
Turn on the switch on the main panel labeled "bridge main." I'm not sure that it is what it is (you said neither the lower helm nor the upper works, correct?) but it is worth a try.
Activate the switch at the lower helm that say "horn."
If that doesn't work then look closely at the breakers in the ER.
If none of those things help it's time to get out the voltmeter.
Some of the wiring on my 400 is "creatively" done. A lot of the switches on my FB helm don't do anything at all. My Auto Pilot and DSM stayed on 24/7 when I bought the boat, I wired a switch into them.
I think the biggest weakness of my boat QC wise, is how they rigged the wiring. I try to fix things as I go along, but there are a lot of things they could have done better.
One thing I did that has really helped is to run the third leg of my charger to the genset start battery. I was always fighting a dead battery on the generator before that. I also reconfigured the battery set up with a dedicated start bank and house bank. Much better.