Purchased a 1999 Gulfstream Conquest in May. There are 3 brand shore batteries, all brand new. The rv acts as if only 1 of the shore batteries is active. I tested the voltage at the batteries with a volt meter after plugging in overnight. All 12 V. I unplugged and ran a fan on the shore batteries for several hours, expecting this to not be much of a drain on 3 batteries. Now the 12 Volt system is pretty much dead. Checked the voltage, and the single battery under the stairs is at 8.5 V, while the other two show -12 V ( not sure why it would have minus voltage). There is a relay or something connected to the two batteries at the back which looks like it is in the off position, I threw that into the on position. Checked all cables for corrosion. Checked the ground wire from the two back batteries, filed it till clean and reconnected. Anything you can recommend to check next ?