So, had to wire tail light from bucket all the way to the taillight.  The wiring from headlight bucket to foot brake pedal was removed from harness and wiring 
from foot to tailight shorted.  It was evident someone had tried to work on it and didn't see the shorted area.  Lucky for me, I had an old DT360 harness, so just harvested the yellow/green wire for repairs.  

Diagnosis:  The frame of the bike was in direct, as in zero clearance, to the fender.  The previous install smashed the tail light wire F L A T.  I made a new
harness extension and now the light works as expected.   BUT, I had to reroute it.   That seems odd though, not being able to use the wiring tunnel. 

So, my question for you DT1 experts, is the fender mounted correctly and how did you wire your tailight harness?  
The DT1 is new to me, so please let me know what you think.

New Routing: 


Fender Mount: 





 

That rear fender is off a DT1 E or DT2/3 . The mounts for a DT1 B or S are different too .
I had a look at the clearance for cabling on my DT 1 B , and it isn't a lot , maybe 5mm .

Does this look like the right one? I noted some of that hardware in the partzilla listing.  I actually see the fender/frame indention from wire in 2nd pic. 

Ebay Link to Fender

The fender seems tough enough I may be able to put a 1/4" cylinder on a marked area and hit it lightly w/hammer.   IE, bend a cylindrical path to the wire tunnel of fender. 

That Ebay fender is the correct one for a B or S model . It even has the correct fittings for the rear mount .