06 3500 turn signal issues

[RWherley]

I have a 06 3500 and when you turn on the fourways, or left turn signal it causes the left marker lights to flash too, but if you turn on the marker lights the issue goes away and everything works fine until you turn the marker lights off again. This problem is only on the left side of the truck, the right side doesn't do it. The truck has a flat bed on it with trucklite 40 series LED lights in it, I've tried putting old non LED lights in the bed and it doesn't change anything. I've disconnected the wires going to the bed and the flashing is definitely coming through the power wire for the left side marker lights. Any ideas?

 

[seafish]

Its fairly common on 3rd gen trucks for the brass contacts in the MFS (multi function switch) to wear down and then the brass particles mix with the factory dielectric grease causing multiple unselected operations to occur during use.

The MFS can replaced or simply removed, cleaned and reinstalled.

 

[Ozymandias]

Check the grounds of both, marker and indicator lights. Seems it pulls the ground through the sidemarkers.

MFS is also a possibility

 

[RWherley]

I was under the impression that all the lights grounded back though the body controller, as ever light I pulled from the original bed harness all grounded through the harness, or did I miss something?

 

[Ozymandias]

Grounded in the engine bay around the battery's*, many ground points inside the cab too.
No ground through the BCM, only positive there.
Also one ground strap from left battery down to the frame, outside of the steering gear.

*some in front of the battery's to the fender, some behind to the fender, passenger side one to the fender.

 

[RWherley]

Thanks, I'll check these things out and see where it gets me

 

[sag2]

If you do a search you should find several posts in removing the multifunction switch and cleaning it. Easy and free to try.

 

[RWherley]

So I figured it out and boy is it stupid, this truck relatively new to us and the previous owner had installed a transmission temp gauge in a pile pod. But to light said gauge he taped the wires for the left front marker lights and ran it the whole way back into the cab though the fire wall. And that wire was the cause of the issues

 

[Ozymandias]

Oh how I love these hacked jobs...
I hope the rest of the truck is in better shape then this.