Running lights and dash lights don't work.

My truck would just shut off. No check engine light, however the dashboard light come on dim, both turn signal is lit solid and high beam light is lit. When I do turn on my lights, all lights on the dash turns off, but the chime still work. Cranks normal, wont start. I plugged in a lower end OB2 scanner to see if it would give me something. Ironically, as soon as I plug it in, the dashboard goes to normal, truck starts up like its brand new, drive fine with the scanner still plugged in; unplug problem resurface. If u put a high end scanner(the 7-9 grand), the prob is still there, but the device reads no connection. After I took it home, I unplug the ICM, I hear all the modules cycle, like a reset. Plug it back in and I have a brand new truck (for 24 hrs it seems like). I did replace the ICM. It works well for 2-3 weeks, now the problem is back. Any ideas before I start throwing away money.

Oh a few shops I went to, the mechanics first words were WTF

Hi - I have a technical question. I think I need a part for a 1998 Tahoe - however I want to make sure. I have an issue with my lights now
switch in OFF position HEADLIGHTS ON BUT NOT REAR
switch in 1st position headlights on and rear but no dash/radio
swtich in full position HIGH BEAM LIGHTS COME ON click high beam swtich lights turn off - no dash or radio lights.

Checked all fuses so figure do you think it's the switch box - is this correct?

Hi - thank you for the quick reply

When the switch is in the off position only the headlights work - thats it - is this right?

Last night I checked the dimmer switch (off, 1st and 2nd click) and it was the problem with dash lights did come on with the lights in the 1st position. (Duh) However the high beams do not work.

When I put the switch in the full 2nd position (12 o, clock) all dash/running lights but no headlights. I click the high beam button and it go to high beam only with all other lights.

If I release the dome overide button (to turn on lights auto when door opened) the lights do not turn off unless I push button in and turn the key and release.

I replace the ICM out of process of elimination. I had replaced that when I had initially bought the truck. It was still under warranty so I trade it at no cost. It did work for like 3 weeks without an issue. With the new ICM, yes the problem is the same today.

1996 Chevy Tahoe V8 Four Wheel Drive 147k miles

How do I know when to replace the headlights or fuse on my 1996 tahoe. To me they look a little dim at night while driving.

Ok -will get back to you tommorow. Thanks!

The original one was purchased about a year ago. The original was part of a major tune-up I did. (Originally I replaced distributor, cap-n-rotor, TPS, MASS air flow, etc

Would a bad ground cause the dash to act the way it is currently?