Seems to me like you would need to do the following:
1. Find out what the current draw is on each lighted Menard's vehicle - I don't have that spec but I'm guessing it's in the 500 mah range.
2. Multiply that figure by the number of vehicles you want to light to figure out your total amp draw.
3. Purchase an ac/dc buck converter that accepts 5-16 acv input with a 4.5 volt (fixed or adjustable) output rated for more than the total current draw you calculated in #2 to connect to your transformer output.
4. Connect the ac/dc buck converter output to some sort of terminal block and run a port from that to each lighted vehicle.
5. You will need to purchase a barrel jack converter (5.5/2.1) to go from wire leads to barrel jack output to connect to the barrel jack of each lighted vehicle.
6. You will then have to splice in a switch from your control panel to the outputs to the vehicles. It's not clear to me whether you want to control each vehicle separately or all at once, so you may need to adjust how many switches you need and exactly how they are wired in. If you want to control each vehicle independently, the switch would have to be wired in after the terminal block. If for all of them at one time, the switch would go in before the block.
