Ok, so here's what I have. 2005 Dodge Ram 1500 Laramie, 5.7L I've highlighted my main question but left everything else normal to give you background on what I've done.

I got a transmission light on. Did the cluster code trick by holding down the odometer button, turning the key to run, and making a note of the code. "C Code" "3d 03". Couldn't find it online, so I hooked it up to a snap on scan tool at the local shop. Got the code "Brake transmission shift interlock output circuit shorted / open"

Downloaded the 2005 DR Service manual. I've started doing the troubleshooting tests to check for Ohms and continuity. 2nd test listed shows checking ohms for Cluster C1, Pin 3 (page 2905 FSM) to the signal wire (Page 2973 FSM) going to the BTSI solenoid. Nothing. No Ohms, and No continuity. The wires look flawless, no damage that I can see, but they disappear into the dash, so I can't trace the wires all the way back. Both wires are the exact same color. Blue and yellow. Part of me was second guessing that I must have probed the wrong wires, but the schematic doesn't lie. The black/red wire grounds like it should.

I tried making sense of the wiring diagram, and it appears that this wire comes straight out of the Gauge Cluster and goes straight to the BTSI. Since the wire is broken "somewhere" where I can't reach it, is there any good reason I can't just make a new jumper wire directly from the gauge cluster to the BTSI? I have no idea if there's a splice or if the wire goes elsewhere, so I'd rather not guess about this. Anyone good at reading wiring schematics that can verify this for me?

Another simple test I did was to unplug the BTSI completely, and have been able to shift the car into reverse and all the gears in drive with it running, so it must be disabled but in the "open" position so this doesn't really affect my ability to use the truck, but it's super annoying to have a dash light on and a system not working how it's supposed to be. I still have to depress the brake pedal to shift it out of park. Also, if there was another problem with the transmission, I'd like the light to come on for THAT problem rather than for this BTSI small problem. Any help would be appreciated! Thanks!

 

The newer dodge rams were recalled due to bad BTSI so this thread might help someone else out in the future when they do a google search. Not sure if it's because of the wiring though. I think their service was on the solenoid it's self.

 

So did you get your fault fixed?
How do it?

 

I haven't figured it out yet. I didn't have continuity on the input voltage side, so I soldered a fresh jumper wire to replace the original wire. Now the Ohms are showing what they should be according to the troubleshooting guide. Now I have continuity and if I check with a multimeter, the wire shows 12v however if I put a load on it with a test light the voltage drops to zero pretty fast.

I'm going to have to wait till Thursday to get the fancy snap on scan tool and try to remotely activate the solenoid and check with a test light if it will light up. The field manual says to do this with the Chrysler scan tool, but I don't have one of those. Just turning the key and starting the truck doesn't seem to give any voltage to the solenoid.

It's leaning towards 1 of 2 diagnosis. One is that the gauge cluster has an internal problem and will need replacement, and the other is the BTSI solenoid is bad. I haven't hooked the solenoid directly up to 12v yet, because there isn't enough room inside the connection to touch each pin without risking a short. The thing that sucks is that if the cluster is bad, there aren't any people advertising gauge cluster rebuilds for this problem, so I'd have to either buy a brand new one, or find a replacement. But I'm not sure if a junkyard replacement will be compatible. I think they're flashed with the VIN of the truck.

If anyone knows about cluster compatibility let me know.