2004 2500 HD Duramax left turn signal always on.

[Screwderado]

Was driving the other day and noticed my left turn signal was constantly on . Checked all bulbs even replaced a few just in case . I unplugged relay and still left turn was on. Didn't see a reason to replace it since at the time it didn't seem to be the problem. Now after a few days of this I noticed the dash warning lights blinked on as I was driving . Like the truck was being started. The Multi-display even went into the block pattern boot up. Right turn works fine and sometimes left will blink until I step on brake light. then it displays always on ( sometimes left will go out when driving a while) really weird issue. I fear my ECM is about to go out. The only thing not stock about this truck is a aftermarket Kenwood radio professionally installed . and some aftermarket turn signal lights in front with LED's but no mod to wiring. Thanks in advance for any insight on this issue. I guess I should also add I have indicators on the side mirrors.

[Jsdirt]

First place I'd be looking is the front LED's. Electronics failures there can make strange things happen. I'd try hooking up the stock light if possible, just to rule that out.

 

Also, dual filament bulbs can sometimes bridge the brake & running lights with a bad filament that lands in just the right spot. That will do equally strange things too. Double check battery connections - make sure they're clean and tight first, to rule that out as well.

[Doug_Scott]

Just to add a bit to Jsdirt post, pay attention to the bulbs on the left side that come on with the daytime running lights as well, specfically the ones that also have the signal on the same physical bulb. The issue can be either the bulb or the socket. Can also be something as stupid as having the wrong bulb installed. Sometimes a single filament bulb has been forced into a dual filament socket. The single terminal will connect the 2 circuits together.

Do not worry about the ECM, it has nothing to do with lights. And as always, check grounds.

[Screwderado]

Thanks for your help I am looking into eliminating the LEDs and checking the bulbs again.