First of all, I bought this Blazer knowing it needed a new transmission and i changed it on my back. Couldn't have done it without this site!

So now I am going to tackle a less critical (for now) issue...
video link: Electrical issues in 2000 S-10 Blazer. - YouTube

Description:
Instrument cluster, odometer, radio only work when headlights are switched on and DRL sensor is covered making vehicle think it is dark out. Gauges go crazy with clicking noises if dome light is turned on or door locks are used from either driver's or passenger's side. Finally, the shift indicator light on the instrument cluster only shows up in PRN but not D321.

Where do I begin? I checked fuses on dash and under the hood.
I have looked up some of the wiring diagrams thinking it might be a ground issue, so that is my planned next step.
I also see that the ignition switch powers many of these components, and that these vehicles have troubles with headlight switches too.

Any advice would be much appreciated!