My first objective with vehicle lighting was for them to appear as realistic looking as I can. I made the decision to use 1½ volt 1mm micro bulbs for correct size and appearance. The majority of the 1mm bulbs are actually closer to 1.5mm so I drill out the headlights on my vehicles with a #53 drill. The micro bulbs fit loosely in a #53 hole. The 1.5mm headlights are equal to 6" 1950s headlights.
For taillights I use red .020" & .030" diameter fiber optic strands and yellow for running lights.
My second objective is to have the vehicles easily movable around my layout to change the appearance of my layout. That requires a special connector for power between the road and the vehicles. The connectors in the roads or parking areas need to be as unobtrusive as possible so as not to be noticeable when there is no vehicle over the connector.
Finding a manufactured connector to do what I was trying to do isn't going to happen. I decided to make my own vehicle connectors. Having a good stock of K&S Brass made it easy. 1/16" (.0625") K&S brass tubing has a wall thickness of .014" and a ID of .035". A 1/32" (.032") K&S brass rod fits perfectly into the 1/16" brass tube making a very good connection.
Cutting the 1/16" tubing to lengths of 1¼" to 1½" works very good for the female side or road connector.
Drilling a 1/16" hole into the road is simple with the correct tools. I have two sets of long drill bits, one with 6" long bits and one with 12" long bits. The 6" long 1/16" drill bit works for most of my connectors using my small 4 volt battery operated Craftsman 4 volt drill. I drill two 1/16" holes ¼" apart where I want the vehicle to be and insert two 1/16" brass tubes with #26 solid wire soldered in one end for power. I use super glue on the brass tube to anchor it flush with the surface. Using a scratch awl to slightly flare the tube makes them easier for the .032" rod to find the hole.
The end of the brass tubing can be touched up with paint the same color as the road surface to hide it from view.
Here are several of my vehicles with the .032" diameter brass rod contacts that can be placed in any of the 90 locations on my layout.
The Public Safety vehicles have three contacts, the third contact is for the flashing beacon. Not all of the vehicle locations have the third contact for the flashing beacon.