I have a 2000 Blazer and one day I started the truck and the headlights started dimming and getting brighter while running. I also was hearing a clicking sound under the dash and hood. Here are a few symptoms:

Open door and dome light starts flickering on and off.

Putting key in ignition makes the BCM door chime start to make wierd and different sounds.

Clicking noises under hood.

Dash lights flickering.

Dome light flashing on and off.

At various times everything will start working normal and the door chime sounds like it normally does. I can start the truck and it will run fine for a bit then the headlights will start flickering again and the ABS and security lights will come on and the BCM will start chiming different again.

The positive post on the battery was coroded and I cleaned that connection and it started to work fine for a bit but now its doing that same thing again.

I don't think it is a blown fuse because the truck will run fine intermittently.

Just wondering if anybody had some ideas on what might be wrong and what to check for. Thanks in advance for any suggestions.

You are losing voltage or ground.
Start at battery and check proper voltage and battery cables and ends.
Make sure you have good grounds and that the charging system is charging good.

Then start checking voltage on up to fuse boxes.

What is the battery voltage?
What is the charging voltage?
How old is battery?