2005 Sierra - All instruments except speedo and tach randomly dropping to zero, all warning lights come on, while driving.

[troverman]

So as of yesterday, my 2005 Sierra 3500 with the gas engine started doing something weird with the instruments. While driving down the road, all gauges except the tach and speedo drop to zero, and all warning lights come on. The truck continues to run just fine. If I wiggle the key in the ignition switch, usually the gauges will come back and the warning lights extinguish. Now I'm seeing the amber Key with Padlock symbol staying on at all times though. My truck is a work truck with crank windows, no frills. I had the cluster replaced 3 years ago and all has been fine. I did replace the radio with an aftermarket, but that was two months ago and no problems, no harnesses cut. Could it be the ignition switch? Would it be the tumbler portion or the electric switch portion?

[troverman]

I pulled the cluster and the connector looked good. Pulled the column shroud and removed ignition switch harness. Connection looked fine but lock tab was slightly broken. Still seemed tight. Reassembled everything and turned on ignition...everything was normal for about 30 seconds (engine off, key in ignition position)...then suddenly all the gauges fell to the zero position. Bizarre. Later I tried again and I have no interior done light, even manually turning on dome light switch. The engine still starts and runs; I have radio and hvac, but cluster is totally dead, all interior switches are no longer backlit. 
 

ignition switch? Some master fuse? 

[troverman]

Update and bump. Apparently nobody has seen this issue before. The truck for the last two days is definitely having erratic behavior...you can drive it 40 minutes and it is perfect, everything is fine. Then abruptly, for no reason, all the warning lights come on, all gauges (except tach and speedo) go to zero, but the truck continues to run perfectly fine. Last night it did that, I drove like that for several miles and pulled over. Shut the truck off, restarted it hoping everything would go back to normal...but instead the entire cluster did not work at all. The truck ran fine, the cluster was backlit, but not one gauge worked at all and the odometer and PRND did not even come on.

 

The one thing in common I have found is that the moment the instruments act up...whether the cluster remains partially working or not working at all, the interior dome light will not work. You cannot turn it on from the switch by the headlights, nor will it come on when you open the door. As soon as the instruments start working again, the light works. Meanwhile, the HVAC and radio have never had a problem. And the gauges may randomly start working again, mid-drive, so its not like once they go off, they remain off until a restart.

 

I'm thinking either a ground or the ignition switch. I had decided the ignition switch couldn't be the problem because of the dome light also not working, but I forgot that they are tied in...if you open the door and then shut the door, the dome light delays for 30 seconds and then shuts off. But if you get in and start the engine, the light goes off instantly.

[txab]

Check all your body grounds. Clean them up. Check the condition of your battery cables as well and the connection at the batt. Cables can fail internally. One model year did have quite a few people post that they had them replaced to clear up issues similar to yours. Not saying this is your problem, but should be checked out, imo.

[troverman]

Thanks Txab for the suggestions. I have thought about the body ground straps, although I would expect problems with the blower and radio as well if that were the case. I will look at the one under the truck (cab to frame) and the one under the hood (cab to engine). I may just replace them and the ignition switch and go from there. Neither are terribly expensive. It appears that you are in TX where rust is not an issue...I'm up in NH where they throw the salt down hard every year with all the snow we get. My truck is solid but rusty underneath; the grounds may be pretty corroded.

[txab]

Doesn't take much to cause electrical gremlins. Grounds caused an issue with my ECBM.  This is where I'd go until someone else chimes in with another idea. Your ignition may the issue too