Turn Signal Problems

[Westo]

My truck came with no front composite lights and a flasher unit removed with the cable cut before the connector. I just got finished putting on all the parts and wiring everything back together but the turn signals are not working. The first time I turned the right signal on it worked front and rear, but turning it to the left did not. Nothing happened when I turned on the hazards, and now even the right doesn't work. The indicator light on the turn signal stalk turns on when the signals are engaged, and I've checked all the bulbs around the truck and they look to be intact.

After these first problems, I noticed the front composite lights didn't have the ground loop installed. I attached that on both sides but I still have the same issue.

Any ideas as to what the problem could be or troubleshooting steps are appreciated.

 

[M813rc]

You're on the right track - check the ground on all the lights and the flasher unit itself, any bad ground in the system does odd things to the lights, like letting them flash sometimes, or flashing the wrong bulbs.
The flasher itself may also have given up, some tend to be very easy to kill. The signal arm may also have an internal problem.

If you have the luxury of spare units to swap out, that can ease the diagnosing. Good luck!

Cheers

 

[Westo]

I was able to test the connections between most things, and they all seemed intact. The only thing I don't think I can properly check is the flasher. I tried taking it out and connecting it to a 24v power supply and using a multimeter to check the outputs, but I imagine it needs a load to work properly. It only drew .03 volts and had no output.

 

[Westo]

As I've been working down the chain of switches and things, I noticed that the horn gets its power from the same light switch output as the turn signals. I've had a problem in the past with the horn sticking on, so I took it off and tested some things there. I found that there's an extra mystery cable on the horn. It's not on the wiring diagram or in the TM for replacing it. I attached that page to this post.

The two with the plugs are the normal 25 and 26 cables which are on the diagrams, and the grounding loop type one is the unknown. It goes through a couple connectors then goes into the same sleeve as the other two. It is not connected to ground or the horn power. The loop was on one of the bolts between the mounting bracket and the horn.

The horn power cable seems to be correctly wired, and the issue with it sticking is somewhere on the ground side so probably not related to the turn signals.
If anyone knows what this cable does or also has it on their truck information would be appreciated.

 

[Westo]

And it gets more confusing. The cable labeled F on the 3 switch light control provides power to the park lights and horn as well as the turn signals when the switch is in service drive. The horn and park lights work on my truck. But when I test the voltage on that cable, I always get zero.

I've also had weird behavior when I test its resistance to ground, but it's probably just bad testing on my part. The first time I tested it, it showed a short to ground. After removing the horn, it was 6.5 kOhms. Now, without having done anything except reconnect the batteries, it has no connection at all. Really not sure what to make of all this.

All things considered I'm pretty sure at this point that it is the flasher unit, but I keep getting weird readings like this that make me think it might be something deeper in the system.

 

[Westo]

Figured it out... was indeed bad testing. Had the multimeter set to AC power when testing voltage.

 

[Westo]

Another update. Thought I had all my issues fixed so I got a new flasher unit and connected it. As soon as I turned on the left turn signal the flasher made a loud pop and some nice smoke. Did more testing and eventually found a short in the harness between the turn signal switch output for the front left and the light harness connector up there. Turns out my alternator was rubbing on the wiring harness right after it comes out of the driver's footwell.

Here's a picture of the general position of it. I think the main reason this happened is that the mounts seem to be bent in a way that slants the rear end towards the left side of the truck. I encountered this earlier as well when replacing the fuel drain drain line from the filter, which had to be routed under the alternator rather than next to it.

 

[Mogman]

Another update. Thought I had all my issues fixed so I got a new flasher unit and connected it. As soon as I turned on the left turn signal the flasher made a loud pop and some nice smoke. Did more testing and eventually found a short in the harness between the turn signal switch output for the front left and the light harness connector up there. Turns out my alternator was rubbing on the wiring harness right after it comes out of the driver's footwell.
View attachment 906126
Here's a picture of the general position of it. I think the main reason this happened is that the mounts seem to be bent in a way that slants the rear end towards the left side of the truck. I encountered this earlier as well when replacing the fuel drain drain line from the filter, which had to be routed under the alternator rather than next to it.

Common issue with the 400A alt.

 

[Westo]

Common issue with the 400A alt.

Rubbing against the wires, or being sort of sideways?

 

[Mogman]

Rubbing against the wires, or being sort of sideways?

Rubbing the wires and mounting issues, if you have the resources you should replace the 400A with the 200A, if not make sure ALL the mounting bolts are tight and in good condition.
The engine is mounted "crooked" in the engine bay so the alt not aligning with the body would be normal.

 

[Westo]

Rubbing the wires and mounting issues, if you have the resources you should replace the 400A with the 200A, if not make sure ALL the mounting bolts are tight and in good condition.
The engine is mounted "crooked" in the engine bay so the alt not aligning with the body would be normal.

I don't have the resources now to replace it so I'm just going to try to make it work for now. I'm going to be pulling the alternator out so I can get to the harness to repair it. Are there any common ways of mitigating the abrasion issue? Moving the harness out of the way seems difficult since it's stuck in one spot because it goes through the body right next to where it's rubbing.