Motorcycle Repair: Tail light, test light, tail light

Question
1996 Dyna Low Rider, - I'm writing to ask this question because my boyfriend has tried everything and refuses to take the bike into the shop for fear it will cost him a fortune.  I would like to keep him safe on the road when we ride.  Here's the problem I hope you can help:  All electric works fine except the tail light running light only - break light is fine).  My boyfriend has replaced the tail light housing. He has replaced the bulb.  He has checked the service manual and has traced/checked the wires with voltmeter.  Power is getting to the tail light because the breaklight works.  Any suggestions?  

Answer
The brake light and the tail light work independly from each other. So what that means is the brake light can work, but not the tail light. The tail light receives its power from the key lights breaker. You should have a good ground since the brake light works.
Start with a test light at the bulb, if no power follow the wires back to the plug and to the source of power until you find the problem. You probably have a short inthe system.
Good luck and happy riding
Mike