My batter isolator sudenly stopped working. It still charges the starter bettery, but it wont charge my Yellow Top. The starter bettery is at 14+ volts, so that's working ok. But the Yellow Top is only at 9 volts. I thought the isolator was broken so I changed it. But it wasn't it. So I thought It has to be one of the fuse. Wasn't that either. Anyone has any idea what else it might be? Thanks.
I think you might have to get your yellow top charged up or you might have damged the cell in it. First when you use different batteries, the strongest battery goes in the back and the smallest goes for cranking. I would get that battery tested, like at autozone. If your connections are good and the isolator is good it has to be the battery. Good luck.