Gordon,
If you've got 13.9 v at both the battery and ignition buss bars and the headlight mod is installed, the voltage drop is occurring has to be between the ignition buss and the headlights. With the mod installed, the headlight voltage comes from the ignition buss bar, through the headlight CB (probably #25) and then to high and low beam relays (pin 30) you added as part of the mod. The output of those relays (pin 87) should go directly to the headlights. If voltage is low for both high and low beam, it would indicate a resistive contact in the headlight relay (CB25). If that's not it, I would suspect a faulty ground at the headlights as the high and low beam voltage paths are separate between the new relays and the headlights.
Good luck,
Steve