I am trying to help someone who is having car issues.
They bought the car back in Feb and everything was working fine...no issues. But then recently out of the blue all the dash lights are on and the fuel guage, A/C and the reverse lights aren’t working anymore.
He was told by people that the BCM/SJB is shot because of the notorious water leak. He replaced it with a working one from ebay and everything is still the same. The SBJ he got has the exact same numbers.
I thought it might have been an electrical issue but he mentioned that he didnt change anything.

Could anyone suggest something he can check or do to fix this?

 

simple cheap things first: make sure the battery is good, fully charged

 

Are you saying lights only not working on the the fuel gauge and A/C or are the two not functioning as well?

 

Reverse lights check; Fuse 59-30amp and Fuse 63-30amp in BEC panel, right front engine compartment. Check also the following fuses; Fuse 44-10amp, Fuse 67-30amp in BEC;

 

I asked him about the fuses and he said that he checked everything and all of them are okay.
This one has me stumped.
I wonder if houtex might know something since hes a fountain of knowledge haha.

 

My fuse checks are based on a 05. Wiring diagrams differ per model year. Therefore without Model year, engine and transmission specs, researching any wiring diagrams or other info is pointless. Good luck in your mission.

 

re: different years...

'05 and '06 are close, but the thermostat housing thing alone in the '05 diagrams messed me up when I needed to figure that out. The book's wrong on that one for me. As but an example. My '66 Tbird was a tweener car, half 65 and half 66 and all sorts of confusing on the wiring and transmission... funtimes, that one.

Anyway. To the problem at hand... *checks the '05 wiring anyway...*
http://iihs.net/fsm/?d=40&f=Reversing%20Lamps.pdf
This is the reverse lamps. We'll use this as the example, and from that, perhaps get a clue. Not sure, here we go anyway.

The reverse switch, either manual or automatic, comes off circuit 359, GY-RD. It goes to the engine controls in one direction. It goes back to the PCM in the other. The PCM then uses the network communications to talk to the rest of the car. Which includes the instrument cluster (IC). Notice how the SJB is NOT YET part of the equation. This is because it's not on the HS CAN. It's on the MS CAN. HS is used for Priority communications, engine, transmission, that sort of thing. The MS is used for 'not so important' things like the radio and... lights.

So. The IC then is the pass through for the PCM to 'talk' to the SJB. This is why the Instrument Cluster is important, and 'married' to the rest of the system. And so it is that the IC passes through the status of the reverse switch to the SJB. And in that, the Low Current Board (LCB) is then told the reverse switch is on, and it then turns on the reverse lights.

QED, Vis a vis, etc and such like that, don't'cha know, quite.

I'm not having all that great a luck with the rest of the things listed. The wiring diagrams are... fun. Suffice it to say that I think the LCB in the SJB is still the culprit, even the 'new' one. Do we know where he got the 'new' one? Perhaps it was bad out of the box... It doesn't seem to be anything else, given what I'm looking at in the diagrams. Or maybe it needs to be programmed with the car? Or it could be the HS CAN or MS CAN wires are having issues.

But then again.. it could be the Instrument Cluster's not happy. It is the pass through for all that stuff, seems like I'm reading... I hope not. Not that I hope it's anything, actually, but it has to be something, right? Right.

Might gotta get a good wiring diagram and a multimeter to check the wiring out. And a better shop manual than what we've seen online, here or at IIHS. And for that stuff.. well, here:
Maybe it's worth the money, if you don't/can't have a shop do the work to figure it out. Otherwise, the nightmare of google and its plethora of unrelated search returns and incorrectly worded search terms might be in order, or the library as Eric O. says. One wonders if the Houston Public Library downtown might have such things... I *have* done that before, btw! Wayyy back when, but sure thing. Think it was on the SVO... Loong drive down there for 5 pages of info, but when ya needed it back then... uphill.. both ways... in the snow*...

Anyway. 'Bout all I got. Seems it's either the SJB's bad outta the box... or the wiring is messed up somewhere... or... yeah, maybe the Instrument Cluster's toast. Let us know, be interested to hear what it winds up bein'...

/ *-Yes, peoples, it's snowed here a few times in my life...
//Not sure it'll happen again down here anytime soon...