You're OK, you didn't, or couldn't have done anything by "messin" around with the fuel drain
Here's what I suspect is going on,,,, your batteries are probably low, you have too small a charger to charge them and Certainly too small to run the GlowPlugs.
Leave the charger on overnight, it is actually connected to both batteries. 6-7Amps is a pretty low charge for 2 low batteries so I'm going to assume that if you had a bigger charger it would charge at a higher rate (What is your chargers capability?)
Of course there's lots of other things it could be, but getting a full charge into your batteries might do it. Make sure the terminals are all cleaned, greased & tight. Next would be to take them out and have each one Load Tested to be sure they're good.
Winters arrival brings unseen problems to light, good news is, it sounds like your GP system is working