Here is another solution to the problem. I had 17V at the battery and replaced many light bulbs multiple times until I resolved the problem. It was related to the relay next to the R/R. I did not have any connectivity from the battery to the monitor wire harness at all. So I opened up the relay housing and found out that the relay was stuck open due to rust. I cleaned it up and it worked fine after that but eventually I should replace it. That relay connects the monitor wire to the battery. Here are some pics of the relay.
