It's probably a combination of voltage drop (38 year old wiring and switches) old sealed beams and bad grounds.
Check and clean the brass headlight contacts and sockets and check the grounds are good first.
If still dim ? A new set of headlights (wagner or GE are good if you not going 100% original) and relays will cure the problem, I use a similar one to this http://www.truckpartsproshop.com/dual_headlight_relay.html
paint it black and mount it next to the voltage regulator (looks stock)
But any two "bosch' Type 4 pin relays will work.
here's a diagram http://www.humanspeakers.com/audi/headlight-simple.htm
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