The Isolator/Emergency Start is a solenoid that is not energized (I checked yesterday). The solar panel can be eliminated as suspect because several years prior a serviceman shorted out the solar panel and I removed the solar panel and pulled it's fuse in the BCC. Also, I had the parasitic drain before and after the solar panel malfunction.
I took the vdc readings within 4-5 minutes of engine start.
The diesel and coach batteries are less than 2 years old and I have had to replace all 4 batteries about every 2 years $$.
Could this problem be connected to when, in 2005, I had Sear's convert the series 6vdc batteries to parallel 12vdc batteries? Where possible I have hand traced battery cables to their intended destinations and not found anything obviously wrong.