Just so you guys have an idea what I'm working with:
1989 with a 4.2 I6 recently set up with a Howell TBI kit.
Here's what happened:
Everything was working great for the last week, turned over instantly, ran wonderfully. Yesterday I dropped a screw down my defroster vent above my dash, so I took apart the dash to try and get it out. After I got the screw out I put the dash back together (basically just screwed it back in place). When I went to start up my Jeep a little later, it wouldn't turn over. The starter doesn't even try. The gauge on my dash shows in the red by the "8" volts however I got my battery tested (it's a week old) and they said its fully charged and perfectly fine.
Is there anything I may have touched while taking apart my dash that would have caused this? The lights on my dash are very dim when I turn the key, but my headlights seem to be at normal brightness...
With a multimeter on the resistance scale, measure between a ground point on the dash to the chassis.
You should read close to zero. A few ohms is ok.
I removed all the coverings (instrument cluster, middle [radio, a/c controls, etc], and glove box.
Strange though, there was a ground wire where the radio would be, I don't have one installed, that the splice had become disconnected. I connected this and the Jeep started. I put that part of the dash back on and it would NOT start again. So I removed the cover checked that the ground was still connected, but now not won't turn over again even with that ground connected...
Okay, update! My Jeep randomly started after letting it sit for the weekend, before any work was done today, but the dash was still dead.
Cleaned every ground I could find (I had done this last week, but I went over everything again), I took out my dash/ignition fuse (tested it again with a multimeter to confirm it's usefulness) and cleaned up the ends of it since they had some residue on them. Then, I swapped fuses with another 15 amp fuse just for kicks (at this point I was willing to try anything). Also, I had taken out all my gauges and had the leads cleaned. After that, I tried to find any wire connectors and tried to make sure they were connected firmly.
Not sure what fixed it (probably the fuse cleaning and gauge cleaning, again) but it starts up and my dash seems to be brighter (normal) again.
So fingers crossed that we're good to go. Gotta thank my awesome girlfriend for the help (she probably won't see this, but you never know...)
Thank you everyone for the advice and help. It's been incredibly helpful.