Broken wiring in tail lights

[Argosy74]

My Argosy t/t 1974 '24 has a broken black wire in the passenger side tail light assembly [stop / turn bulb - not the b/u]. That's why the light won't work (it did recently - new bulb too). I took off the cover and opened the light assembly and saw the black wire free (about 3" then a metal crimp - I assume this is where the assembly was originally hooked up to the long wire).

I can not find the "other" section of the black wire. I started from the pig tail and notice the wires run through the street side frame and disappear into the "under belly" of the trailer.

Does anyone know how this model was wired for tail lights? I mean, where do the wires run?

I was thinking of splicing in at a convenient spot. It seems like I would have to cut into the aluminum somewhere (ahhh)

Any other ideas?

I can not find nor get to the wire (I tried a vacuum - no luck).

Also - any ideas on where to get replacement lights? The lights are about 4" x 9" in a rectangular shape. The manuf was Peterson Manuf out of MO - still there but they no longer manuf that light assembly nor cover - per co. e-mail).

Any help appreciated.