Hello there. I am new to PMDG, recently purchased the DC-6 for P3Dv4. I am really enjoying it and slowly figuring out all it's intricacies. I'm starting to use it for VA flights, which means I'm to the point where I don't think I'll screw up too badly! 

After startup today I noticed a warning light that I hadn't seen before. I had to search for the appropriate breaker to reset. A first in my many years of simming, very cool!

Thanks for a great product!

That's cool!
What was the warning? Do you know why it occured.?

AFE had completed "Before Start" checklist, I had started all 4 engines and AFE had completed "After Start" checklist.

I noticed the red light on the top left of the main panel (instrument power failure or something like that) was still on.

I switched views to the breaker panel and found the related breaker tripped. I reset it and the light went out.

I completed the flight without further issue, so I guess I really don't know for sure what caused it. 

You need to switch on in the overhead the power to electrical instruments. Otherwise you would not see for example fuel pressure.