Dashboard electrical issue, trying to fix it myself - FIXED IT (kinda)

2014 Cascadia

Earlier today, the whole row of lower dash swithes from the emergency flasher all the way to the AC controls went out. Backlight is out, and the switches don't do anything. No backup lights, no mirror heat, nothing. The check engine light is on and the display is beeping contnuously and annoyingly and saying "Engine Braking Problem" because it can't read the engine braking strength switch (which is one of the row of switches that went dark) and is getting confused. The check engine code is 973, which is again because it's not sensing the switch. The flasher still works, btw, just not the black switches.

An interesting data point is that in the few minutes that the switches were blinking out, there was a static sound from the left door speaker.

So I've concluded that the problem is with whatever wiring is supplying power to that bank of switches. Is there a fuse that handles them? Might the left speaker wire somehow shorted with the switches' power wire, thus making that noise? Or is it something entirely different.

I know the mechanics will probably charge me a grand for digging in there and changing a $20 part or a $2 wire, so I'm gonna take off the front panel and do some passive investigating. But if anyone has experienced a similar issue or has experience with dash wiring please let me know. A wiring diagram would be great, also. Thanks.

Update: all the switches are out, even the sleeper ones. Gotta be a fuse

 

That's awesome, I'm learning already. So what would you recommend, pulling all the switch banks or at least looking behind them? Are they linked to a fuse by any chance? None of the glove box fuses seem to apply, and they are all good anyway.

Also: ALL the switches don't work. If half of them worked, that would make it easier to isolate the break in daisy chain, but they all seem to be out, not even the green backlight.

 

Sadly, it's not that fuse. I tried swapping it for other fuses, no luck.

As you said, the switches are daisy chained, from right to left, all leading to what seems to be the master unit, the one with the emergency flasher. It has a ton of connections coming out of it. Pic enclosed. Seems there might be another daisy chain from this master unit to the sleeper side switches.

I wish I had some AAA batteries for my old voltage tester, that way I could at least check if the fuse F5 is getting power at all.

Any other ideas?

 

Update: success!

I downloaded a very dense and technical manual about the cab electrical system, and learned that:
A: these are called MSF switches on a CAN bus. (Sorry mr. Uncleal, not J1939. That controls the more serious stuff like the engine.)
B: the box with the flasher triangle is the MSF Master. It controls all the other so called slave switch modules by a three wire connector. It has multiple inputs for those connectors.

My particular version of the master controller seemed to have two slave switch connectors going into it: one for the important front switches and one for the rear ones. So I tried pulling out the rear switch connector and voila! All the front switches came back on! The check engine light and the beeping went away, and my engine brake works again.

I guess the signal wire running to the rear switches has a short somewhere, and it was confusing the whole digital system, flooding it with white noise so it couldn't "hear" all the other switches. I will have to track it down eventually, but meanwhile I can keep running! It'll be a bit annoying not being able to control lights from the bunk, but that's a project for some other day, when I'm stuck somewhere waiting for freight and bored.

I am so relieved, I was afraid that I fried something expensive. Now time to put the truck back together and go to sleep.

 

Thanks for the correction. You are likely right, the ECU with the flasher triangle talks to the switches with its own code and passes the info on to the main ECU via J1939. It also controls the steering wheel buttons and the turn signal stalk, btw. Modern trucks have their own multiple internets, so complicated. Good thing that I'm kind of a redneck nerd, grew up building my own computers and stuff. I can figure it out.