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2005 gmc 3500 LLY
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Discussion Starter · #1 ·
Hello group, long post.
about the truck:
2005 gmc 3500 LLY stock 218k push button 4x4, cloth sle crew cab. I’m in NY but Truck is from Florida. Owned since mid summer. I have recently replaced the water pump and thermostats.

To the issue:
I’ve got this electrical gremlin that I need help diagnosing.
When I got the truck I noticed that the pass lock light would be dimly lit with key off or on and it’s been like that for awhile. (I had previously posted on here about that). I went out Monday to let it warm up and this started. The truck starts up and runs fine even when it acts up.
The gauges act up and various warnings are displayed. There is clicking noises coming from under the hood. Headlights go on and off. Radio comes on and off. Power windows won’t have power intermittently. It will not allow the 4x4 to shift and the lights on the 4x4 shifter button will not be light. Only the speedo gauge continues working correctly. Odometer will not change mileage while driving when it starts acting up. Heater controls are not affected. This issue is intermittent.
Sometimes I’ll get in and drive no issue will happen. I stop somewhere for an hour then drive away and it acts up. Not sure what the trigger is.
I’ve been wiggling wires under the dash and steering column and it didn’t seem to effect it. It does its own thing.
I’ve check various ground and ran a ground wire from the battery to the cab post. The engine ground to the cab is present and in good shape. There are no codes but the scanner will lose communication with obd when it starts acting up. I’ve also disconnected the radio head unit and interface (aftermarket) to see if that changed it (it didn’t).

I took videos so you can see what is happening. but I don't know how to post them. Maybe I could in a private message or on Facebook.
If anybody had some insight please comment or message me. It’s appreciated. Thank you.
 

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There have been issues like this that have been resolved by checking/fixing the grounds specifically the battery ground.
 
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99% chance it's a grounding issue IMHO. Just start repairing and replacing the grounds, and make sure you do a really nice job, with super-clean connections and dielectric grease. And solder all the connectors, no crimping allowed!

Maybe start by replacing the two main battery cables. That would be fairly cheap. Of course, even cheaper would be to clean/inspect all the existing grounds.
 

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2005 gmc 3500 LLY
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Discussion Starter · #5 ·
99% chance it's a grounding issue IMHO. Just start repairing and replacing the grounds, and make sure you do a really nice job, with super-clean connections and dielectric grease. And solder all the connectors, no crimping allowed!

Maybe start by replacing the two main battery cables. That would be fairly cheap. Of course, even cheaper would be to clean/inspect all the existing grounds.
I cleaned the grounds in the engine bay and the ones under the drivers door on the frame. I also took a ground wire from the battery to the post on the cab. I'm going to clean the grounds inside the cab today. I didn't realize how ground sensitive these trucks are. Thanks for the reply.

I'll be posting a video later today as well. Thanks GBsierraSLE for the link.
 

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2005 gmc 3500 LLY
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Discussion Starter · #6 ·
I happened to come across a forum where a guy found out that his air bag module that's under the drivers seat was causing all kinds of weird electrical issues due to corrosion. So I looked at mine and sure enough, it was covered in corrosion and was wet. I unplugged it and it seems to be normal right now so hopefully that was the issue.
 

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Discussion Starter · #7 ·
I did clean up a bunch of grounds and the interior functions are working much faster and smoother.
I just have a very dim pass lock light on. Which has been on since I got the truck. The light is so dim I can't even see it in the day time only at night and flickers ever so slightly.
 
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