It's ripping cold here, well below zero and at startup, I noticed the airbag light on, no interior lights,power windows, horn, heater blower, turn signals and maybe more that I haven't discovered. It did struggle to start. I'm guessing I blew a fuse, but where do I start to look? PDC or fuse panel?

 

Batteries don't like cold, especially old ones. I never try to start a vehicle below zero without preheating it first. Too many things working against you and doing damage.
Tricks we do up here is to dilute your oil with a small amount of gasoline at shut down. It evaporates out as the engine warms up. And if the battery is weak, turn your head lights on for a little while. The load will cause heat that warms the battery. We also slide little BBQ grills under them for some heat.

 

It's not a battery issue. It started and I let it warm up a bit then shut it down. WQent back about an hour latter and all the electrical works as it should although the air bag light was on. Never was before. Took a drive, let it sit and the light had gone out. I'm guessing that a relay might have hung up but that's only a guess. Seems like all is well now......

 

Moisture in the electrical and bitter cold along with the stuff mentioned in the second post were/are most likely your problem(s).
Had some of the same problems in MO when the weather got uber (single digits or lower) cold.

 

It's -40F where I am... Just plug her in and she fires up fine. -30F is where the XJ starts to struggle a bit on start up if its not plugged in.

 

Damn that's cold! -40, whew!

 

Best $25 you will ever spend, instant heat too!

 

Think you hit the # there.
Worst time I had getting started I was working nights on the MO river early JAN -56, took about an hour to get going, about 200 of the guys owned diesels lots of those were left sitting anti-gel agents couldn't stand up.

 

Ever shear an oil pump drive? I have. Heat your oil!