The house batteries in my trailer did not want to hold a charge anymore. I replaced them with new batteries and I thought that would do the trick. It did seem to make things better, for a while at least.
A month later and the lights in the RV were dimming again. These batteries are brand new so I knew that I must have another problem. I got out my multimeter and started troubleshooting.
I checked the batteries with the cables removed. I had low voltage across the batteries. Next, I checked the voltage coming out of the charging system built into the power center in the trailer. The voltage reading here was good.
I checked the voltage at the positive cable going to the battery and once again found the voltage to be to low. I checked the voltage at the cut-off switch was also low. Yet back at the charging system the voltage reading was right up where it belonged.
Next, I did a continuity check on the negative cable coming from the battery which went to the frame. It showed that it was good.
Finally, I pulled the power center out to check the ground coming out of it and discovered my problem. The wire was extremely burnt from a bad connection.
My batteries were not the root of my problems these last few months. They were not being charged properly due to the bad electrical ground.