Speedy,
Regarding your side markers (as opposed to reflectors), they get power from the closest tail lamp assembly or headlamp assembly respectively. There is a "pigtail" coming from each marker, and these plug into the assemblies.
Now comes the rub--if you don't have the proper receptacles on your tail lamp and headlamp assemblies, you actually have the wrong ones on your car. This is not an uncommon problem on restorations. There were three different US Spec headlamp assemblies, and at least two tail lamp assemblies--manybe more. They look the same from the outside, but the wiring and assembly are different. It is rare for a parts seller to know these differences.
You can, if you want to, purchase a receptable and splice it into the lamp assemblies to provide a place to plug in your markers. You could obtain the proper lamp assemblies, or you could forget the receptacles, and do a cut and splice job. Lastly you can replace the markers with reflectors.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored