Jim...

I'm not sure that the springs in the Kadee trucks actually do that much. I
have a lot of Kadee trucks and also a lot of unsprung/non-equalized trucks
(cast metal) and the latter work just as well as the Kadees as long as all
of the wheels are touching the rails. So, if the bolsters can be insulated
from the trucks and the wiper placed between the insulation and the truck
(and hard wired to the circuit), the wipers would be pushing down on the
axles along with the weight of the caboose.

On a caboose project that I am scratchbuilding from styrene, I glued a brass
washer to the bottom of each bolster to pick up power from the trucks; each
of the washers has a wire soldered to it leading to the lighting system. I
am using non-equilized trucks with metal wheels which allows power from the
wheels on one side of each truck to get to the bolster (obviously, the
trucks have to be mounted so that the insulated wheels are on opposite sides
of the car). If you can substitute different trucks on your caboose, you
might be able to shave the bolsters down enough to insulate them from the
body with some styrene and then add a brass washer to feed the electrical
system along the same lines. You can then eliminate the axle wipers.

When I tested my caboose on the layout, the conductivity wasn't that
constant, causing the lighting system to flicker. However, I plan to add the
lighting circuit you mention which will eliminate that problem.

BTW, your model sounds like the old MEW (Model Engineering Works) Grasse
River caboose....

Jack Burgess
www.yosemitevalleyrr.com