im having a problem with my 99 blazer
the guages and interior lights and locks will not work unless the light sensor is covered up and the headlight switch is turned on.
checked fuses and their all good. replaced the multi-function switch twice with new parts each time. tried a new light switch and new sensor but still acts the same. seems like it all started after i had the trans repaired. could it be a bad ground? bad ...TBC? ...PCM?

 

I actually have a very similar problem, ever since i got a rebult transmission my 4x4 works off and and stuck in 4hi, my interior lights are glitchy, my overhead unit glitches off and on

 

yea after the guys changed my transmission i noticed a buncha spilled trans fluid around the tbc area. maybe it shorted something out?
i forgot to mention another thing about my blazer. the stereo never keeps its memory for the time or audio settings

 

problem solved!

Last night i popped the hood and checked for power going to the fuses. I clamped my 12v tester to a ground, and tested the fuses. Found out there was no power going out from the 50 amp RAP fuse. So i disconnected the battery, then unbolted the fuse block. I turned it upside down and i seen 2 wires that were connected to a plug. One wire was broke off and one was still connected. The wires were very corroded.
I unplugged the plug and seen it was un-usable. So I cut the plug off and the corroded ends of the wires off, then crimped a piece of new wire to each end. Then i crimped a female spade connector to the ends of the new wires. I then plugged the connectors to the 2 plug terminals. Bolted the fuse block back in and connected the battery. started the blazer up and everything works normal again!

all the gauges come on
lights work
power locks work
radio works and keeps its memory

thank you! to the people on blazer forum