[dab1950]

Walt,
To answer your question about "how to get to the wiring inside the unit"; there
are channels or trim pieces at the corners of the walls or roof & walls. However,
take it from me there is no slack in those internal wires. I dealt with an elusive
electrical problem involving the rear tail lights and the rear marker lights.
There's almost no slack to pull to the outside.
Not sure what tools you have to use or how much experience you have with
wiring but here's what I would do.
Tools to gather:
hemostat(for holding the short stubb of inside wire coming thru wall)
heatshrink(for covering a solder splice)
soldering iron(small) and 60/40 solder for small jobs.
wire stripper and cutter.
To do:
Use the hemostat to grab a wire stubb coming through the wall on the insulation.
Avoid grabbing the bare wire because you will be heating the
wire. Hopefully, there is enough bare wire that you can twist together
with the color matched wire from the new fixture. But before you twist
these wires together, put a 1 or 2 inch length of heatshrink on the wire
from the fixture. Now twist the wires together with as much overlap as you
manage. Apply solder to the tip of the hot iron to get a bead of molten solder
on the tip of the iron. Now touch this molten bead of solder to the twisted
joint of wires and at the same time, touch a strand of solder to the wire joint
and move the solder strand so the flux melts and cleans the wires.
In another second or two, the solder will start melting to fill gaps in the twisted joint.
Be sure there is solder on all sides and the wires are covered. Now once the
solder has cooled, remove the hemostat and slide the heatshrink over the joint making
sure no wires are exposed. Now use the soldering iron to lightly touch the
heatshrink and keep it moving. The heatshrink will begin shrinking at little at a time.
Keep moving the iron until the heatshrink is tight to the joint. This will prevent the wire
joint from shorting to the metal wall of the TM. Repeat the same on the next wire.

Feel free to post or send PM any new questions.

Doug.