[nightscapespaul]

When installing a lighting system, put all runs on the 12v tap of your multi tap transformer. When you have the entire system insalled, go back and make your voltage corrections. You may have to do this twice. As you add more fixtures to a system, you put a higher demand on the transformer, causing more voltage drop. You can't get true voltage measurements until the entire system is up and running. You should try to achieve 10.8 to 11.5 volts to each fixture.
If you use this procedure, you should have less problems with your lighting systems.