[vettestr]

Hey Dirk,
The gang has you on track but thought this might help you check the ground and voltage. If you look at the headlamp plug here is the ground reference. Colors never seem to match so twist connector so one pin is horizontal when the other two are vertical. The horizontal pin should be the ground . If the ground is on the bottom the plug the pin to the right is high beam (looking at plug from the bulb side of the connector. Check the left also to prove I am correct.

Test voltages at the pins then move the negative meter lead to another known good ground like the alternator case. If the voltage changes you have a poor ground. If no change move on to voltage checks. System voltage with engine running and lamps on hi beam with cooling fans on high should show a min. of 13.9 to 14.2 VDC at say 2000 RPM. happy hunting Jeff c