Temp gauge fluctuation

[natron80]

Hey, this is my first post, but I have done a lot of searching and found a lot of valuable information here.

I recently bought an 89 Blazer S10 4.3 4x4 to get me through the winter after my last car was stolen and stripped.

Anyway, my problem is this... Last night I was working on it trying to get the 4x4 working (hasnt worked since I bought it). All it needed was a vacuum line. So I fixed that and 4x4 works fine now. I was driving it around the yard a bit testing it out and I noticed that my temperature (digital dash) would go from 200 degrees (where it always runs since I put in the new thermostat), down to nothing (no bars on the temp gauge). I know for a fact that the engine temperature isn't fluctuating this much because I touched the temp sensor and it's still hot, as are the heater and radiator hoses.

At first I figured it was just a bad temp sensor, but when I disconnected it and tried to start the truck it wouldnt run. I plugged it back in a reset the computer. Still does it. It doesnt seem to run any different when the temp gauge reads no temp, but it might be dumping fuel and I just cant tell. If anyone has had this happen before, please let me know how to fix it. I'm thinking it might be a bad connection that got disturbed when I ran the new vacuum line, but I really don't know. Any help would be greatly appreciated. Thanks a lot.

Nate