...I'm fairly certain, that since the original regulator was of a (slowly) cycling thermal element design, one would see either 0 or 12 Volts on the regulated output line, (the (long-term) AVERAGE of the line was 10V - this was apparently perfectly adequite for the instruments, which have an extremely slow response time). I gutted my 1800ES's when it failed, and replaced the thermal element with a modern fixed output electronic regulator. I would expect that's what the ones available from IPD have.

As far as the symptoms after failure...I would expect there to be two sets...one for if it failed at 0V output (supplied gauges would read zero) and one for if it failed at 12V output (guages would read high).

Hope that helps.