Jimmy Booth of PBL explained that the "grounded" pickup for the passenger car lights relied on the spring and steel screw to pass electricity to the lights, so he suggested soldering a wire from the pickups to a brass stop pin soldered to the car floor. I made this modification to my cars and took some quick handheld photos along the way to document what I did. You can click on any of the pictures to see a full size image.
The first step is to take off the correct truck. The truck grounded to the frame has a squared off oval as a bolster, as you can see in the second picture, but this is hard to see with the trucks on. It is easier to spot the soldered wire that feeds the other side of the lighting circuit, marked with a red arrow in this picture:
This is what the bolster the truck stop pins look like with the truck removed:
At this point I scraped some paint off of one of the pins with an X-acto knife then solder a short piece (about 1.25") of very flexible wire to the pin. Naturally my worst solder job out of four cars is the one I photographed.
The next step is to figure out the orientation of the truck wiper and solder the other end of the wire to it. This is the orientation the wiper will be in when the truck is reinstalled, but the screws to put the truck back together are towards the floor. This length of wire will allow me to reassemble the truck upside down, then flip it back over lengthwise to this orientation to screw it back down.
The truck is upside down and I have just screwed the platic piece that holds the truck wipers in place back down. The 1.25" wire gave me just enough length to flip the truck over this way.
And here is the truck mounted back on the car. There is a bit more wire than I would like, but I felt no drag from it, and I don't think there is too much chance of it fouling anything since the truck simply doesn't move that much even when swung to its extreme in both directions.