Note: Looks like you might not need this post now. I'll leave it just in case it helps anyone else, but I think you are a "step" ahead of it now
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Just got in from bringing a hot cup of coffee and a homemade cinammon roll out to my manual step. Just kidding, but I can feel your pain! One time I had just gotten a cargo trailer and was about to set out on a journey. Hooked up to the Chinook in the storage bay and all the lights checked out (Hallmark cargo trailer, which has like TWENTY-EIGHT running lights/tail light/license plate light). Headed out without the lights on as it was broad daylight, then around 6 p.m. (in the middle of the Mohave, no services in a jillion miles) turned on my lights. Buddy following me was like hmmm, no trailer lights and NO TAILLIGHTS on the Chinook. (Also no marker lights on the Chinook which was a big clue, but I digress.)
Now, we could have pressed on with him following me and eliminated most of the worry, but dangit, my Chinook was *broken* and I wanted if fixed!
We had pulled into a rest area and had to go in the truck section as we were both driving RV's and towing too. It was packed. I seriously had to have him guard my legs (that were sticking out as I dove under the rig) to make sure no semis ran over it. The parking was a bit of a free-for-all in the "non-designated" spaces.
I already knew from when I had originally wired my trailer hookup (years ago) that Chinook had used the Ford trailer light fixture to power the Chinook taillights (I know,
). But the marker lights weren't working either?! I hunted and groveled in the gravel with a headlamp on, increasingly vexed. Eventually I remembered the "Marker lights" fuse position in the Chinook-added fuse box under the dash. Aha, that fuse was blown (not to surprising as I think it is 7.5 amp and it was powering all the incandescent marker lights on the Chinook, the taillights on the Chinook, and all the lights on the trailer (also incandescent). But how were these connected?! (I had towed another trailer successfully for years but that had LED lights and not so many.)
Long story short, Chinook used the Ford trailer harness for the taillights (and of course it also powered the trailer lights) (so that's one run of relatively skinny wire from front to back of the rig), THEN they ran a wire (skinny) from there up along the driver's side frame rail, through the driver's stepwell (under the black step insert), and to the Marker light fuse (so that's a second long, long run), THEN they ran that wire back to the rear marker lights (so that's the THIRD super long skinny run). Oh please. So no way could I just put in a larger fuse. But at least I had the problem figured out.
What I did for that night was remove about half of the "marker lights" on the trailer (they were sort of click-out cartridges), and that got it below the threshold and through my drive. Then I ordered all LED replacement lights for the trailer (which I wanted anyway). At that point it was below the 7.5 amp threshhold and all was fine (interestingly, on the Amazon review page for the LED trailer lights, were many other people with Hallmark trailers wherein the monstrous number of incandescent marker lights had blow their car's trailer light fuse).
Another option would be to re-wire with thicker wire and perhaps eliminate two of the long runs by putting the marker light fuse at the rear (well-labeled!), but the LED light solution also works.
Anyway, so you have traced the wire to going around behind the shower. Then in my experience (have had my Chinook somewhat down to the bones) the wire will run up along the chase that is above/behind the upper couch cabinets. When it gets to the TV area I can think of two options: Down the pillar and then somehow into the cab (but I have no seen any other wires do this; they have either been underneath the coach and gone through the stepwell, or have gone in above the cab), or up the pillar and into the cab via the Ford hole in the chassis cab. I don't have the electric step, but they did run the wires in similar fashion to get to the generator start in the over-the-driver switch panel in the overhead (but on the passenger side).
Not saying you need to do this, but to visualize: If you remove the pillar, then you see that Chinook completely kept the chassis cab as delivered by Ford (which I kind of like for strength). Thus there is a white metal Ford flange on each side that runs up from floor to ceiling. It kind of "wraps around" so that it's running perpendicular to the outside walls. This flange (one on each side of rig) has a hole right up near the corner where it turns to make the Ford cab roof. A bundle of wires go into this hole on the driver's side (I forget now what they are all for, most are Ford I think). A smaller bundle goes in the hole on the passenger side (including Chinook speaker wire, generator start wire, and a couple of others). I *think* these all or mostly run to the headliner, but maybe one goes to the ignition cue for the step? Is there any override switch or anything in the headliner as a stepping stone?
Otherwise, there are some wires that go through that cabinet wire chase, then down the pillar and out through a hole in the floor (that is behind the pillar). If so you might find the wires running along under the black plastic cab stepwell cover.
The pillar is kind of a bear to remove, but thanks to some description by a member here (augh, why can't I remember his name, New Mexico member), I was able to do it. Holler back if you are going to remove the pillar and we can give some tips. If you don't obviously find the wire in the driver step area, or the overhead cab panel area, pillar removal might help you to see everything.
BG