Running/ Marker Light Troubleshooting

[Stilwellian]

I have a 68 Tradewind. All of the running/marker lights work fine except for two. One on the front and one on the side. I have doublechecked the bulbs and they are good. There appears to be continuity between the power wire and the bulb fixture. The bulbs will not turn on however. Are there any troubleshooting tricks to finding the problem or is it easier to just replace the entire light assembly? I am surprised that there are no threads that I can find here detailing how to troubleshoot an individual running/marker light not working. Surely I am not the first to deal with this problem.
Thanks.

[overlander63]

Check for corrosion/rust on the power contact in the base, and the spring that keeps the contact pressed against the bottom of the bulb is still in good shape.
You did check to make sure the assembly is grounded, right?

[Stilwellian]

I checked for voltage between the hot lead and the bulb receptacle..... it was soooo low compared to a check between the hot lead and the ground source as in the trailer outer skin. To troubleshoot, I ran a simple patch wire between the grounding rivet mount for the lamp base and the bulb receptacle and voila....let there be light! The connection between the ground wire and the ground source must be corroded. A little touch of solder and a little patch wire will fix the issue without having to replace the entire assembly for now. Thanks for reminding me about the ground test. I was just checking continuity. Booyah!