Battery Switch Fail

[Mathewfamily]

I am getting some voltage surging when the key is one. I put an ohm meter on the batteries and noticed that there was a voltage drop surge on one of the batteries when the key is on. Nothing running but the BIG screen. It is only coming from one of the batteries so I swapped power to the other battery to illuminate the battery. The same thing happened on the opposite batter when swapped. I noticed some corrosion on one of the lugs on my battery switch so I pulled the wires off and sanded the corrosion away on the lug base and the terminal ends. Once I put them back on the lug I was no longer getting power to that lug of the switch. I have no idea what I did wrong. Has anyone had issues with the battery switch and should I just get a new switch? I have no idea what is surging the system. I turn on the blower and you can hear the surge when it happens, it lowers the speed in the blower for a half a second then normal for a second then down and repeat.
Does anyone have any clues where this voltage drop could be coming from? What could be pulsing like that? When the motor is running it tends to dip/pulse when in idle as well. I unplugged the power to the Indmar controller panel to illuminate the motor from the pulsing equation and the pulsing was still there. I am at a loss. My heater seems to be not working at times too. Any help would be greatly appreciated...

[curver900]

what type of switch do you have?
how many batteries are in the system?
did it just start doing this or did you do something and then it started?
what is the voltage of the batteries at rest? switch off
what is the voltage of the batteries when running ?

This should help get an idea... of where to start...

[MLA]

Does anyone have any clues where this voltage drop could be coming from?

The alternator produces voltage and the battery stores it. You indicated you used a meter and identified a voltage drop. Fallow that circuit back toward its source until you find where the voltage drop is no longer there.

Good chance that the visual corrosion you saw, has wicked down the insulation of the cable(s)

[Mathewfamily]

Good point on the wicking. I will see trace this wire down and replace it.
I don't know where to begin to find out where the voltage drop or surge is coming from. The engine is not running when I tested the battery and found the drop/surge/pulse. I know it is not coming from the alternator or anywhere else on the engine since I had unplugged the motor harness and it was still there.
The batteries at rest, 2 of them, 1 was at 12.02 and the other was around 12.48.
After reading some today on resting voltage, maybe the whole issue is the batteries!