Docking Lights Problem GS-201

Our '99 GS-201 is having a problem with the docking lights. I found that with the 2 docking lights on, my Garmin depth/fish finder alerts me to a big drop in voltage. It goes from 12.5v with the lights off to 9 volts when the lights are turned on with the motor off. Typically when I turn on the dock lights the Garmin shuts off. When I power it back on, it shows the low voltage. The Garmin is wired to the accessory circuitry. Also, when the dock lights are on, the little red light on the switch is only dimly lit. The dock lights look like they're sufficiently bright. The battery is only about 2 years old.

I've opened the switch panel and cleaned the contacts for the light switch and accessory switch. As a side note, I was amazed how easily some of these wires just broke off at the push connector when I gently moved the connector or wire. I replaced 3 connectors. I checked all the other connections to make sure they weren't about to break.  I also cleaned the connections at the dock lights circuit breaker. All the connections at the ground terminal strip seem good.

Any suggestions on how to proceed with this? How much voltage drop is normal when turning on the dock lights (I think these bulbs are halogen but I'm not sure). I also tried the lights while cruising and experienced the same problem and voltage drop. I measured the voltage at the horn with a multimeter and confirmed what the Garmin was reporting. Even running the motor trim only drops the voltage about 1 volt or so. Interior lights, nav lights also drop it by only about 1 volt. Could this be something as simple as replacing the dock light bulbs?

We don't typically boat at night and even if we did we wouldn't need the dock lights for long. But I would still like to fix this if possible. Any help is greatly appreciated.